cache.h: add repository argument to oid_object_info

Add a repository argument to allow the callers of oid_object_info
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>
Reviewed-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -3638,7 +3638,8 @@ int diff_populate_filespec(struct diff_filespec *s, unsigned int flags)
 	else {
 		enum object_type type;
 		if (size_only || (flags & CHECK_BINARY)) {
-			type = oid_object_info(&s->oid, &s->size);
+			type = oid_object_info(the_repository, &s->oid,
+					       &s->size);
 			if (type < 0)
 				die("unable to read %s",
 				    oid_to_hex(&s->oid));