Fix bug 1360 (diffs with parent diffs)

Review Request #1186 — Created Oct. 31, 2009 and discarded

Fix bug 1360 (diffs with parent diffs)

In pure-git setups, post-review with parent diffs was broken because
the parent diff wasn't being generated properly (it diffed master and
the work tree instead of master and parent).
Set up a pure git repo (i.e. no git-svn or git-p4 or anything). In a local clone, have branches A and B such that B^ == A and A^ == master, and B modifies a line that A modifies (so `git diff A..B` applied to master doesn't apply cleanly). Run post-review with --parent=A and verify that the diff appears correctly on the site (previous behavior was to show an error because the patch didn't apply).
  1. Dan Savilonis provided a large comprehensive change for improving our branch detection. Can you update your post-review from Git and see if the new code works for you?
    1. As it turns out, that change fixes the bug too. Forget about this one then. Le sigh.
    2. Thanks anyway :)