Fix arc + svn + delted binary file with properties + image heuristic

Summary:
See IRC. This fixes an issue when deleting an SVN file that ends with one of the extensions in the regexp, which may only affect newer versions of SVN.

Possibly we shouldn't have this heuristic, or should move it elsewhere or make it more explicit, but at least stop it from being broken for now.

Test Plan: Ran `arc diff --only` in a working copy with a deleted binary file ending in ".jpg".

Reviewers: btrahan, nh

Reviewed By: nh

CC: aran, mbishopim3

Differential Revision: https://secure.phabricator.com/D6893