Summary:
Ref T2222. Make the "EditPro" controller accommodate diff updates, and support the transaction type. This one is pretty straightforward.
Also make `revisionPHID` in the comments table nullable to fix the "Edit" action.
Test Plan:
- Created new revision.
- Updated revision.
- Tried to do some invalid stuff.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T2222
Differential Revision: https://secure.phabricator.com/D8376
