Parse property change diffs generated with old SVN (prior to 1.5)

Summary:
Fixes T2565. SVN from before June 2008 generates different looking property changes.

See http://subversion.tigris.org/issues/show_bug.cgi?id=3019 for the change.

Test Plan: Added a unit test derived from the report in T2565, made it pass.

Reviewers: chad, vrana

Reviewed By: chad

CC: aran

Maniphest Tasks: T2565

Differential Revision: https://secure.phabricator.com/D5009