commit: add repository argument to set_commit_buffer

Add a repository argument to allow callers of set_commit_buffer to
be more specific about which repository to handle. This is a small
mechanical change; it doesn't change the implementation to handle
repositories other than the_repository yet.

As with the previous commits, use a macro to catch callers passing a
repository other than the_repository at compile time.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

object.c

@@ -217,7 +217,7 @@ struct object *parse_object_buffer_the_repository(const struct object_id *oid, e
 			if (parse_commit_buffer(the_repository, commit, buffer, size, 1))
 				return NULL;
 			if (!get_cached_commit_buffer(commit, NULL)) {
-				set_commit_buffer(commit, buffer, size);
+				set_commit_buffer(the_repository, commit, buffer, size);
 				*eaten_p = 1;
 			}
 			obj = &commit->object;