Hushp1pt 0.8.7 pull1

Hi, 
These patches improve buildbot's integration with Gerrit (repo).  The major improvement lets you use repo with branches other than master (buildbot/repo's branch points to the manifest's branch).  The minor improvement lets your Gerrit event change source just ignore any projects your buildbot is not interested in. 
These patches are working well in buildbot (from tip of branch 0.8.7 with no other local changes) + Gerrit 2.1.8 (an older version, admittedly). 
Sorry the patches aren't rebased and tested on master, etc. I finally recognized that's just not going to happen. Hope this helps. 
Cheers-