Use DiffQuery instead of direct hunk loads in MessageParser daemon
Summary: Ref T5179. Ref T4045. Continue reducing the number of direct hunk loads we perform.
Test Plan: Pushed a closing commit, used scripts/repository/reparse.php --message ... to trigger this logic, got a sensible/accurate result.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Differential Revision: https://secure.phabricator.com/D9288