Further improve line grouping in unified views
Summary:
Ref T2009. This tweaks things a bit more to improve consecuitive groups of added and removed lines.
Generally, it gives us "old, old, old, new, new, new" intead of "old, new, old, new, old, new".
Feelin' real good about having unit tests for this stuff.
Test Plan: Unit tests, looked at diffs in web UI.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T2009
Differential Revision: https://secure.phabricator.com/D11994