R1:d85425e65486

Use transactions in saving comment

Summary: We had a real issue where revision was marked as accepted but the comment wasn't saved.

Test Plan: Reclaim abandoned revision.

Reviewers: epriestley

Reviewed By: epriestley

CC: jungejason, aran, Koolvin

Differential Revision: https://secure.phabricator.com/D2463