setup: allow check_repository_format to read repository format
In some cases, we will want to not only check the repository format, but
extract the information that we've gained. To do so, allow
check_repository_format to take a pointer to struct repository_format.
Allow passing NULL for this argument if we're not interested in the
information, and pass NULL for all existing callers. A future patch
will make use of this information.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>