Enrich "diffusion.commit.search" with identity, status, and message information
This enriches the results from diffusion.commit.search with information similar to the information returned by the "commits" attachment from differential.diff.search.
Also include unreachable, imported, message, audit status, and repository PHID.
Test Plan: Called diffusion.commit.search and reviewed the results, which looked sensible.
Reviewed By: amckinley
Maniphest Tasks: T13197
Differential Revision: https://secure.phabricator.com/D19658