Add basic test coverage for the Subversion parser

Summary:
Ref T4327. Adds the same basic battery of tests to the SVN parser as the other parsers have.

cowsay {{{ THIS IS AN AMAZING DIFF }}}

Test Plan:
Ran unit tests against SVN change parsing.

bwahaha

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4327

Differential Revision: https://secure.phabricator.com/D8016