local hushp1pt change: do not force $PWD on (Windows) buildslave.  See http://trac.buildbot.net/ticket/456.

In our configuration, we run build slave on Windows, using Windows Python, without Cygwin.
But we run many ShellCommands using Cygwin (give the full Windows path to Cygwin's bash.exe in the command list).
Without this local change, bash's pwd returns the Windows PWD (C:\buildslave\something).
Unfortunately, our bash scripts need the traditional Cygwin pwd (/cygdrive/c/buildslave/something) to work right.
Repo build step can work with any Git branch (repo init -b), not just master.
Add config options to Gerrit change source to filter Gerrit events by project name and/or event type.
Repo build step parameter name should be default_manifest_branch instead of manifest_branch