Starting with Bugzilla 4.4.7, the distributed tar files include a .git
directory. Needless to say, unpacking that on top of our own .git
directory results in chaos (including a changed "git remote" URL for
origin).  Exlude the .git directory.

The downside of this is that the pristine-tar diff file will be fairly
large.

This was first used to upgrade to version 4.4.6.