topgit_msg: expose bare branches
Instead of annotating bare branches with "(missing .topmsg)"
(which they are) annotate them more correctly with "(bare branch)"
instead. It's a bit more friendly and more accurate and looks
a little bit less like an error. And truthfully "bare branches"
are tolerated just a bit more than only "missing .topmsg" branches.
Therefore the change makes sense from that perspective and it does
provide more information than the old annotation.
Signed-off-by: Kyle J. McKay <mackyle@gmail.com>