This patch creates a new attribute on the Repository object called source_viewer.  It is an interpolatable string, similar to that of bug_tracker, that allows the Branch: property to link to the appropriate branch in an online repository tool, such as Trac (or even the SVN http interface).

I have this deployed on my company's Review Board server and it seems to be working fine.

I am not familiar with writing automated Python tests with Django, so therefore there are no tests for this patch.