Add basic post-review support for git

Review Request #708 — Created Jan. 18, 2009 and submitted — Latest diff uploaded


Review Board SVN (deprecated)


This patch allows post-review to support git proper.
Manually tested with basic git repositories.

I don't have an ancient version of git svn on hand, so I couldn't test whether the check I added for svn-remote.svn.url is sufficient or necessary to prove something is a git-svn repository.