3 changes to enable git-annex to work correctly with gitolite and GitLab

Hello,

I made these changes to enable git-annex to work correctly with gitolite and GitLab:
- fixed processing of repository urls ending with .git (GitLab recommends urls like that to users by default),
- git-annex-shell command is added to .gitolite.rc (disabled by default)
- command pattern is changed to allow for some characters git-annex may include in its arguments

These changes along with your commits in git-annex branch are also backported to gl-v320 branch of GitLab fork of gitolite - I created another pull request for those.

Best regards,
Oleg