Summary: If someone accidentally pushes a bunch of commits, revisions might get marked as "Committed" incorrectly. This will restore them to their previous state without too much fuss.
Test Plan: Ran the script on some commits to undo them, it seemed to work correctly.
Reviewers: davidreuss, btrahan
Reviewed By: btrahan
CC: aran, epriestley
Differential Revision: https://secure.phabricator.com/D1877
