Add audit entry when code changed after a revision was accepted

Summary: build on top of D2530 and D2540. Add an auditing entry when the code was changed after the revision was accepted.

Test Plan: ran reparse.php manually. It worked at https://phabricator.fb.com/rPHGIT461864d2e09dad04c28505658ef75a979e44d0d3. Look at the latest auditing entry for auditor 'phgit ha directory'.

Reviewers: vrana

Reviewed By: vrana

CC: nh, epriestley, aran

Maniphest Tasks: T201

Differential Revision: https://secure.phabricator.com/D2586