Convert lookup_commit* to struct object_id

Convert lookup_commit, lookup_commit_or_die,
lookup_commit_reference, and lookup_commit_reference_gently to take
struct object_id arguments.

Introduce a temporary in parse_object buffer in order to convert this
function.  This is required since in order to convert parse_object and
parse_object_buffer, lookup_commit_reference_gently and
lookup_commit_or_die would need to be converted.  Not introducing a
temporary would therefore require that lookup_commit_or_die take a
struct object_id *, but lookup_commit would take unsigned char *,
leaving a confusing and hard-to-use interface.

parse_object_buffer will lose this temporary in a later patch.

This commit was created with manual changes to commit.c, commit.h, and
object.c, plus the following semantic patch:

@@
expression E1, E2;
@@
- lookup_commit_reference_gently(E1.hash, E2)
+ lookup_commit_reference_gently(&E1, E2)

@@
expression E1, E2;
@@
- lookup_commit_reference_gently(E1->hash, E2)
+ lookup_commit_reference_gently(E1, E2)

@@
expression E1;
@@
- lookup_commit_reference(E1.hash)
+ lookup_commit_reference(&E1)

@@
expression E1;
@@
- lookup_commit_reference(E1->hash)
+ lookup_commit_reference(E1)

@@
expression E1;
@@
- lookup_commit(E1.hash)
+ lookup_commit(&E1)

@@
expression E1;
@@
- lookup_commit(E1->hash)
+ lookup_commit(E1)

@@
expression E1, E2;
@@
- lookup_commit_or_die(E1.hash, E2)
+ lookup_commit_or_die(&E1, E2)

@@
expression E1, E2;
@@
- lookup_commit_or_die(E1->hash, E2)
+ lookup_commit_or_die(E1, E2)

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

ref-filter.c

@@ -1782,7 +1782,7 @@ static int ref_filter_handler(const char *refname, const struct object_id *oid,
 	 * non-commits early. The actual filtering is done later.
 	 */
 	if (filter->merge_commit || filter->with_commit || filter->no_commit || filter->verbose) {
-		commit = lookup_commit_reference_gently(oid->hash, 1);
+		commit = lookup_commit_reference_gently(oid, 1);
 		if (!commit)
 			return 0;
 		/* We perform the filtering for the '--contains' option... */
@@ -2108,7 +2108,7 @@ int parse_opt_merge_filter(const struct option *opt, const char *arg, int unset)
 	if (get_oid(arg, &oid))
 		die(_("malformed object name %s"), arg);
 
-	rf->merge_commit = lookup_commit_reference_gently(oid.hash, 0);
+	rf->merge_commit = lookup_commit_reference_gently(&oid, 0);
 	if (!rf->merge_commit)
 		return opterror(opt, "must point to a commit", 0);