object: convert lookup_unknown_object() to use object_id

There are no callers left of lookup_unknown_object() that aren't just
passing us the "hash" member of a "struct object_id". Let's take the
whole struct, which gets us closer to removing all raw sha1 variables.
It also matches the existing conversions of lookup_blob(), etc.

The conversions of callers were done by hand, but they're all mechanical
one-liners.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/refs.c b/refs.c
index b8a8430..cd297ee 100644
--- a/refs.c
+++ b/refs.c
@@ -379,7 +379,7 @@ static int filter_refs(const char *refname, const struct object_id *oid,
 
 enum peel_status peel_object(const struct object_id *name, struct object_id *oid)
 {
-	struct object *o = lookup_unknown_object(name->hash);
+	struct object *o = lookup_unknown_object(name);
 
 	if (o->type == OBJ_NONE) {
 		int type = oid_object_info(the_repository, name, NULL);