branchCounts: Improve branch name safety checking and specification.
branchCounts: Improve branch name safety checking and specification.

It's a good idea to prepend "refs/heads/" prefix to the branch name. If
not done, in case of an ambiguous refspec, the wrong branch will be
selected.

pombredanne/go-vcs,pombredanne/go-vcs,alexsaveliev/go-vcs,alexsaveliev/go-vcs