Summary: Ref T2683. Throw a more tailored exception to allow callers to distinguish between bad refs (which are expected, if users try to visit garbage branches) and other types of errors. Test Plan: Tried to view branch "alksndfklansdf". Viewed branch "master". Reviewers: btrahan Reviewed By: btrahan Subscribers: epriestley Maniphest Tasks: T2683 Differential Revision: https://secure.phabricator.com/D9094