Slightly improve prose diffs for text ending in newlines or punctuation
Ref T3353. Currently, if text ends in newlines (or some other types of punctuation) we generate an extra piece at the end which can muck up the algorithm.
Do a slightly better job with this.
Test Plan: Viewed a diff between "a\nb\nc\n" and "a\nb\nc\nd\n", got a cleaner diff out of it.
Reviewed By: chad
Maniphest Tasks: T3353
Differential Revision: https://secure.phabricator.com/D16061