Previously, if there was an error while storing a local
tracking ref, the low-level functions would report an error,
but fetch's status output wouldn't indicate any problem.
E.g., imagine you have an old "refs/remotes/origin/foo/bar" but
upstream has deleted "foo/bar" in favor of a new branch
"foo". You would get output like this:

  error: there are still refs under 'refs/remotes/origin/foo'
  From $url_of_repo
   * [new branch]      foo        -> origin/foo

With this patch, the output takes into account the status of
updating the local ref:

  error: there are still refs under 'refs/remotes/origin/foo'
  From $url_of_repo
   ! [new branch]      foo        -> origin/foo  (unable to update local ref)
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>