Always render comment panel in Diffusion commit view

Summary: I'm going to stop showing changes for commits which touch 30,000 files, but still want to show the comment panel.

Test Plan: Looked at commits, saw comments. Mashed "Z"; haunted mode worked.

Reviewers: nh, vrana

Reviewed By: nh

CC: aran

Differential Revision: https://secure.phabricator.com/D4729