Merge branch 'jk/ref-filter-flags-cleanup'

Merge branch 'jk/ref-filter-flags-cleanup'

"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