Merge branch 'ab/gc-reflog'

Fix various glitches in "git gc" around reflog handling. * ab/gc-reflog: gc: handle & check gc.reflogExpire config reflog tests: assert lack of early exit with expiry="never" reflog tests: test for the "points nowhere" warning reflog tests: make use of "test_config" idiom gc: refactor a "call me once" pattern gc: convert to using the_hash_algo gc: remove redundant check for gc_auto_threshold