R1:07db53b6f8db

Optimize loading draft revisions

Summary:
This is killing us since D3615.

Maybe we should also change `differential_inlinecomment` index <commentID> to <commentID, authorPHID>.

Test Plan: Checked queries at **/differential/** with comment drafts.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3667