Hadn't known vc-refresh-state gets into my find-file-hook
irregardless.  This won't work with git branches in a detached
HEAD state.

emacs -Q --batch -l vc-git -l log-edit --eval "\
(let* ((dir (make-temp-file \"vc-git-tests\" t)) \
       (default-directory dir)) \
(vc-git-create-repo) \
(with-temp-file \"foo\") \
(vc-git-register (split-string \"foo\")) \
(vc-git-checkin (split-string \"foo\") \"his fooness\") \
(vc-git-checkout nil (vc-git--rev-parse \"HEAD\" t)) \
(with-current-buffer (find-file-noselect \"foo\") \
(run-hooks (quote find-file-hook)))) \
"