Merge branch 'mh/ref-api'

* mh/ref-api: clear_ref_cache(): inline function write_ref_sha1(): only invalidate the loose ref cache clear_ref_cache(): extract two new functions clear_ref_cache(): rename parameter invalidate_ref_cache(): expose this function in the refs API invalidate_ref_cache(): take the submodule as parameter invalidate_ref_cache(): rename function from invalidate_cached_refs()