Accept pushes with arbitrary Git refs
Upstream Git now features "notes", and there's no reason to prevent writes to arbitrary refs, particularly beause we plan to start using them soon (see T13278).
Allow these writes as affecting raw refs.
- Pushed an arbitrary ref.
- Pushed some Git notes.
- Wrote a Herald ref rule, saw "ref" in the dropdown.
Reviewed By: amckinley
Differential Revision: https://secure.phabricator.com/D20420