filter-branch: be more helpful when an annotated tag changes

filter-branch: be more helpful when an annotated tag changes

Previously, git-filter-branch failed if it attempted to update an
annotated tag.  Now we ignore this condition if --tag-name-filter is
given, so that we can later rewrite the tag.  If no such option was
provided, we warn the user that he might want to run with
"--tag-name-filter cat" to achieve the intended effect.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>