PHT's for Differential.

Summary:
Went through this last night, I had to remove some static vars, but didn't see that as a huge perf issue.

Lint

Test Plan: Tested numerous differential pages, creating a diff, commenting, editing.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4617