[travis] Improvements to main script

- Add README.ci
  Suggestions and comments welcome.
- Use the system compiler to get some boot speedup.
- Build log folding.
- Set NJOBS=2 (very moderate speedup)
- Set language to a defined value.
  OPAM itself recommends C, so we follow suit.
- Remove spurious `.opam`test

  No harm in testing we are in the right opam setting even if the
  cache did exist.

  Anyways, it seems that the previous was spurious, as it was testing
  if ~/coq/.opam did exists. I think the correct command would have
  been:

```shell
[ -e ${HOME}/.opam ] || opam init ...
```

  See the log at https://travis-ci.org/coq/coq/builds/198948812 for an
  example.

1 files changed, 22 insertions, 5 deletions

diff --git a/.travis.yml b/.travis.yml
index ab59cf6bf..14573e295 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,7 @@
 dist: trusty
 sudo: required
-language: ocaml
+# Until Ocaml becomes a language, we set a known one.
+language: c
 cache:
   apt: true
   directories:
@@ -14,8 +15,9 @@ addons:
     - aspcud
 env:
   global:
-  - NJOBS=1
-  - COMPILER="4.02.3"
+  - NJOBS=2
+  # system is == 4.02.3
+  - COMPILER="system"
   # Main test suites
   matrix:
   - TEST_TARGET="validate"           TW="travis_wait"
@@ -24,7 +26,12 @@ env:
   - TEST_TARGET="contrib-compcert"
 
 matrix:
-  # Extra is Full COQ build and test-suite with two compilers
+
+  allow_failures:
+  - env: TEST_TARGET="ci-cpdt"
+
+  # Full Coq test-suite with two compilers
+  # [TODO: use yaml refs and avoid duplication for packages list]
   include:
     - env:
       - TEST_TARGET="test-suite"
@@ -75,12 +82,22 @@ matrix:
           - imagemagick
 
 install:
-- "[ -e .opam ] || opam init -j ${NJOBS} --compiler=${COMPILER} -n -y"
+- opam init -j ${NJOBS} --compiler=${COMPILER} -n -y
 - eval $(opam config env)
 - opam config var root
 - opam install -j ${NJOBS} -y camlp5 ocamlfind ${EXTRA_OPAM}
 - opam list
+
 script:
+
+- echo 'Configuring Coq...' && echo -en 'travis_fold:start:coq.config\\r'
 - ./configure -local -usecamlp5 -native-compiler yes ${EXTRA_CONF}
+- echo -en 'travis_fold:end:coq.config\\r'
+
+- echo 'Building Coq...' && echo -en 'travis_fold:start:coq.build\\r'
 - make -j ${NJOBS}
+- echo -en 'travis_fold:end:coq.build\\r'
+
+- echo 'Running tests...' && echo -en 'travis_fold:start:coq.test\\r'
 - ${TW} make -j ${NJOBS} ${TEST_TARGET}
+- echo -en 'travis_fold:end:coq.test\\r'