Merge new string builtin

This adds the new builtin 'string' which supports various string
manipulation and matching algorithms, including PCRE based regular
expressions.

Fixes #2296

Squashed commit of the following:

commit 4c3eaeb6e57d76463e9683c327142b0aeafb92b8
Author: ridiculousfish <corydoras@ridiculousfish.com>
Date:   Sat Sep 12 12:51:30 2015 -0700

    Remove testdata and doc dirs from pcre2 source

commit b2a8b4b50f2398b204fb72cfe4b5ba77ece2e1ab
Merge: 11c8a47 7974aab
Author: ridiculousfish <corydoras@ridiculousfish.com>
Date:   Sat Sep 12 12:32:40 2015 -0700

    Merge branch 'string' of git://github.com/msteed/fish-shell into string-test

commit 7974aab6d367f999f1140ab34c2535cef5cf3b00
Author: Michael Steed <msteed@saltstack.com>
Date:   Fri Sep 11 13:00:02 2015 -0600

    build pcre2 lib only, no docs

commit eb20b43d2d96b7e6d24618158ce71078de83c40b
Merge: 1a09e70 5f519cb
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Sep 10 20:00:47 2015 -0600

    Merge branch 'string' of github.com:msteed/fish-shell into string

commit 1a09e709d028393c9e9e6dc9a84278f399a15f3d
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Sep 10 19:58:24 2015 -0600

    rebase on master & address the fallout

commit a0ec9772cd1a0a548a501a7633be05dab4e5ee46
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Sep 10 19:26:45 2015 -0600

    use fish's wildcard_match() for glob matching

commit 64c25a01e3f7234f220ba13545cf658a7492b1a4
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Aug 27 08:19:23 2015 -0600

    some fixes from review

    - string_get_arg_stdin(): simplify and don't discard the argument when
      the trailing newline is absent
    - fix calls to pcre2 for e.g. string match -r -a 'a*' 'b'
    - correct test for args coming from stdin

commit ece7f35ec5f4093763627d68d671b6c0c876896d
Author: Michael Steed <msteed68@gmail.com>
Date:   Sat Aug 22 19:35:56 2015 -0600

    fixes from review

    - Makefile.in: restore iwyu target
    - regex_replacer_t::replace_matches(): correct size passed to realloc()

commit 9ff7477a926c4572e26171cab3cd42f8086be678
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Aug 20 13:08:33 2015 -0600

    Minor doc improvements

commit baf4e096b22dde3063b85b833795eb570d660ba7
Author: Michael Steed <msteed68@gmail.com>
Date:   Wed Aug 19 18:29:02 2015 -0600

    another attempt to fix the ci build

commit 896a2c2b279a419747bea26102229fbe84534a6f
Author: Michael Steed <msteed68@gmail.com>
Date:   Wed Aug 19 18:03:49 2015 -0600

    Updates after review comments

    - make match/replace without -a operate on the first match on each
      argument
    - use different exit codes for "no operation performed" and errors, as
      grep does
    - refactor regex compile code
    - use human-friendly error messages from pcre2
    - improve error handling & reporting elsewhere
    - add a few tests
    - make some doc fixes
    - some simplification & cleanup
    - fix ci build failure (I hope)

commit efd47dcbda2ca247d58bee56a7774cd75a1062fd
Author: Michael Steed <msteed68@gmail.com>
Date:   Wed Aug 12 00:26:07 2015 -0600

    fix dependencies for parallel make

commit ed0850e2db467362066a3d94e3ececd17c1756cd
Author: Michael Steed <msteed68@gmail.com>
Date:   Tue Aug 11 23:37:22 2015 -0600

    Add missing pcre2 files + .gitignore

commit 9492e7a7e929c03554336be1ddf80ca6b37f53c5
Author: Michael Steed <msteed68@gmail.com>
Date:   Tue Aug 11 22:44:05 2015 -0600

    add pcre2-10.20 and update license.hdr

commit 1a60b933718feb20c0bf7c9e257b8e495014ea1b
Author: Michael Steed <msteed68@gmail.com>
Date:   Tue Aug 11 22:41:19 2015 -0600

    add string builtin files

    - string builtin source, tests, & docs
    - changes to configure.ac & Makefile.in

commit 5f519cb2a2c05213e0a88a7add7af288bc1c1352
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Sep 10 19:26:45 2015 -0600

    use fish's wildcard_match() for glob matching

commit 2ecd24f79500879e2de5bdf1b4c19dd44fc6ac85
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Aug 27 08:19:23 2015 -0600

    some fixes from review

    - string_get_arg_stdin(): simplify and don't discard the argument when
      the trailing newline is absent
    - fix calls to pcre2 for e.g. string match -r -a 'a*' 'b'
    - correct test for args coming from stdin

commit 45b777e4dc85c05cd4a186f4bdcae543c21aaf08
Author: Michael Steed <msteed68@gmail.com>
Date:   Sat Aug 22 19:35:56 2015 -0600

    fixes from review

    - Makefile.in: restore iwyu target
    - regex_replacer_t::replace_matches(): correct size passed to realloc()

commit 981cbb6ddf742a5fe8881af916e7b870b7e6422a
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Aug 20 13:08:33 2015 -0600

    Minor doc improvements

commit ddb6a2a8fdb6aa31aad41e80d5481bb32c6ed8ff
Author: Michael Steed <msteed68@gmail.com>
Date:   Wed Aug 19 18:29:02 2015 -0600

    another attempt to fix the ci build

commit 1e34e3191b028162863d263e9868052f75194aa5
Author: Michael Steed <msteed68@gmail.com>
Date:   Wed Aug 19 18:03:49 2015 -0600

    Updates after review comments

    - make match/replace without -a operate on the first match on each
      argument
    - use different exit codes for "no operation performed" and errors, as
      grep does
    - refactor regex compile code
    - use human-friendly error messages from pcre2
    - improve error handling & reporting elsewhere
    - add a few tests
    - make some doc fixes
    - some simplification & cleanup
    - fix ci build failure (I hope)

commit 34232e152df17a3cfbf0a094dd51d148a4f04e6f
Author: Michael Steed <msteed68@gmail.com>
Date:   Wed Aug 12 00:26:07 2015 -0600

    fix dependencies for parallel make

commit 00d7e781697f53454beb91c1d0fc4b2d28d6e034
Author: Michael Steed <msteed68@gmail.com>
Date:   Tue Aug 11 23:37:22 2015 -0600

    Add missing pcre2 files + .gitignore

commit 4498aa5f576e09634f7f619443e74d2f33c108e4
Author: Michael Steed <msteed68@gmail.com>
Date:   Tue Aug 11 22:44:05 2015 -0600

    add pcre2-10.20 and update license.hdr

commit 290c58c72e22db644ccf6fa9088051644980ed0a
Author: Michael Steed <msteed68@gmail.com>
Date:   Tue Aug 11 22:41:19 2015 -0600

    add string builtin files

    - string builtin source, tests, & docs
    - changes to configure.ac & Makefile.in

1 files changed, 148 insertions, 0 deletions

diff --git a/pcre2-10.20/test-driver b/pcre2-10.20/test-driver
new file mode 100755
index 00000000..8e575b01
--- /dev/null
+++ b/pcre2-10.20/test-driver
@@ -0,0 +1,148 @@
+#! /bin/sh
+# test-driver - basic testsuite driver script.
+
+scriptversion=2013-07-13.22; # UTC
+
+# Copyright (C) 2011-2014 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# As a special exception to the GNU General Public License, if you
+# distribute this file as part of a program that contains a
+# configuration script generated by Autoconf, you may include it under
+# the same distribution terms that you use for the rest of that program.
+
+# This file is maintained in Automake, please report
+# bugs to <bug-automake@gnu.org> or send patches to
+# <automake-patches@gnu.org>.
+
+# Make unconditional expansion of undefined variables an error.  This
+# helps a lot in preventing typo-related bugs.
+set -u
+
+usage_error ()
+{
+  echo "$0: $*" >&2
+  print_usage >&2
+  exit 2
+}
+
+print_usage ()
+{
+  cat <<END
+Usage:
+  test-driver --test-name=NAME --log-file=PATH --trs-file=PATH
+              [--expect-failure={yes|no}] [--color-tests={yes|no}]
+              [--enable-hard-errors={yes|no}] [--]
+              TEST-SCRIPT [TEST-SCRIPT-ARGUMENTS]
+The '--test-name', '--log-file' and '--trs-file' options are mandatory.
+END
+}
+
+test_name= # Used for reporting.
+log_file=  # Where to save the output of the test script.
+trs_file=  # Where to save the metadata of the test run.
+expect_failure=no
+color_tests=no
+enable_hard_errors=yes
+while test $# -gt 0; do
+  case $1 in
+  --help) print_usage; exit $?;;
+  --version) echo "test-driver $scriptversion"; exit $?;;
+  --test-name) test_name=$2; shift;;
+  --log-file) log_file=$2; shift;;
+  --trs-file) trs_file=$2; shift;;
+  --color-tests) color_tests=$2; shift;;
+  --expect-failure) expect_failure=$2; shift;;
+  --enable-hard-errors) enable_hard_errors=$2; shift;;
+  --) shift; break;;
+  -*) usage_error "invalid option: '$1'";;
+   *) break;;
+  esac
+  shift
+done
+
+missing_opts=
+test x"$test_name" = x && missing_opts="$missing_opts --test-name"
+test x"$log_file"  = x && missing_opts="$missing_opts --log-file"
+test x"$trs_file"  = x && missing_opts="$missing_opts --trs-file"
+if test x"$missing_opts" != x; then
+  usage_error "the following mandatory options are missing:$missing_opts"
+fi
+
+if test $# -eq 0; then
+  usage_error "missing argument"
+fi
+
+if test $color_tests = yes; then
+  # Keep this in sync with 'lib/am/check.am:$(am__tty_colors)'.
+  red='' # Red.
+  grn='' # Green.
+  lgn='' # Light green.
+  blu='' # Blue.
+  mgn='' # Magenta.
+  std=''     # No color.
+else
+  red= grn= lgn= blu= mgn= std=
+fi
+
+do_exit='rm -f $log_file $trs_file; (exit $st); exit $st'
+trap "st=129; $do_exit" 1
+trap "st=130; $do_exit" 2
+trap "st=141; $do_exit" 13
+trap "st=143; $do_exit" 15
+
+# Test script is run here.
+"$@" >$log_file 2>&1
+estatus=$?
+
+if test $enable_hard_errors = no && test $estatus -eq 99; then
+  tweaked_estatus=1
+else
+  tweaked_estatus=$estatus
+fi
+
+case $tweaked_estatus:$expect_failure in
+  0:yes) col=$red res=XPASS recheck=yes gcopy=yes;;
+  0:*)   col=$grn res=PASS  recheck=no  gcopy=no;;
+  77:*)  col=$blu res=SKIP  recheck=no  gcopy=yes;;
+  99:*)  col=$mgn res=ERROR recheck=yes gcopy=yes;;
+  *:yes) col=$lgn res=XFAIL recheck=no  gcopy=yes;;
+  *:*)   col=$red res=FAIL  recheck=yes gcopy=yes;;
+esac
+
+# Report the test outcome and exit status in the logs, so that one can
+# know whether the test passed or failed simply by looking at the '.log'
+# file, without the need of also peaking into the corresponding '.trs'
+# file (automake bug#11814).
+echo "$res $test_name (exit status: $estatus)" >>$log_file
+
+# Report outcome to console.
+echo "${col}${res}${std}: $test_name"
+
+# Register the test result, and other relevant metadata.
+echo ":test-result: $res" > $trs_file
+echo ":global-test-result: $res" >> $trs_file
+echo ":recheck: $recheck" >> $trs_file
+echo ":copy-in-global-log: $gcopy" >> $trs_file
+
+# Local Variables:
+# mode: shell-script
+# sh-indentation: 2
+# eval: (add-hook 'write-file-hooks 'time-stamp)
+# time-stamp-start: "scriptversion="
+# time-stamp-format: "%:y-%02m-%02d.%02H"
+# time-stamp-time-zone: "UTC"
+# time-stamp-end: "; # UTC"
+# End: