R1:bed3a9817b8b

Merge author and committer

Summary: These columns holds the same value in most cases which irritates me.

Test Plan: Displayed history with same author and committer, emulated different committer.

Reviewers: hsb, epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D2671