R1:8ab178932903

Improve displaying of very large commits

Summary:
Behave like Differential.

Also save one path ID query.

Test Plan: Displayed very large commit, clicked in ToC, clicked on Load.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3176