Convert remaining callers of lookup_commit_reference* to object_id

Convert remaining callers of lookup_commit_reference* to object_id

There are a small number of remaining callers of lookup_commit_reference
and lookup_commit_reference_gently that still need to be converted to
struct object_id.  Convert these.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>