"git tag --contains" used to (ab)use the object bits to keep track
of the state of object reachability without clearing them after
use; this has been cleaned up and made to use the newer commit-slab
facility.
* jk/ref-filter-flags-cleanup:
ref-filter: use separate cache for contains_tag_algo
ref-filter: die on parse_commit errors
ref-filter: use contains_result enum consistently
ref-filter: move ref_cbdata definition into ref-filter.c