Use prose diffs in Phriction
Summary: Ref T3353. This improves whitespace display of prose diffs and uses them in Phriction.
Test Plan: {F1677957}
Reviewers: chad, avivey
Reviewed By: avivey
Subscribers: avivey
Maniphest Tasks: T3353
Differential Revision: https://secure.phabricator.com/D16062