R1:d7b8bc892b5f

Display revision number in history

Test Plan:
Displayed repository.
Displayed repository history.
Wondered that we actually have bunch of commits without a revision.
Displayed blame.
Didn't display merge commit.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D2840