### Please describe the problem.
I ran forget to clean up dead repos in my map, now map won't run.


### What steps will reproduce the problem?

$ git annex forget --drop-dead --force 
....
$ git annex map

### What version of git-annex are you using? On what operating system?

(xubuntu)
$ git annex version
git-annex version: 5.20140306-g6e2e021
build flags: Assistant Webapp Pairing Testsuite S3 WebDAV Inotify DBus XMPP Feeds Quvi TDFA CryptoHash
key/value backends: SHA256E SHA1E SHA512E SHA224E SHA384E SKEIN256E SKEIN512E SHA256 SHA1 SHA512 SHA224 SHA384 SKEIN256 SKEIN512 WORM URL
remote types: git gcrypt S3 bup directory rsync web webdav tahoe glacier hook external
local repository version: 5
supported repository version: 5
upgrade supported from repository versions: 0 1 2 4

### Please provide any additional information below.

[[!format sh """
$ git annex map --debug
map /media/archive/annex ok
[2014-03-15 09:17:33 CDT] read: git ["config","--null","--list"]
[2014-03-15 09:17:33 CDT] read: git ["config","--null","--list"]
[2014-03-15 09:17:33 CDT] read: git ["config","--null","--list"]

git-annex: user error (git ["config","--null","--list"] exited 126)
failed
git-annex: map: 1 failed
"""]]