R1:0da0632242d2

Display author of last manual diff in summary and test plan comments

Summary:
D2550 is not compatible with D2540.
Example: D2559.

Test Plan: Display commandeered revision.

Reviewers: nh

Reviewed By: nh

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D2567