Silence Mercurial warning for lastmodified query; minor cleanup

Summary:
See https://github.com/facebook/phabricator/issues/102. Commit data may not be available for unpared commits, but we'll raise a warning about $commit_data in that case (the UI correctly handles missing $commit_data).

Also some minor cleanup / UI fixes.

Test Plan: Browsed around hg / git repos, including unparsed commits.

Reviewers: btrahan, killermonk

Reviewed By: btrahan

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1961