localrepo: deprecate 'repo.join' in favor of 'repo.vfs.join' localrepo have an insane amount of method. Accessing the feature through the vfs is not really harder and allow us to schedule that method for removal.

pycompat: move imports of cStringIO/io to where they are used There's no point to import cStringIO as io since we have to select StringIO or BytesIO conditionally.

rbc: empty (and invalid) rbc-names file should give an empty name list An empty file (if it somehow should exist) used to give a list with an empty name. That didn't do any harm, but it was "wrong". Fix that.