commit: add repository argument to lookup_commit_reference_gently

Add a repository argument to allow callers of
lookup_commit_reference_gently 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>

archive.c

@@ -380,7 +380,7 @@ static void parse_treeish_arg(const char **argv,
 	if (get_oid(name, &oid))
 		die("Not a valid object name");
 
-	commit = lookup_commit_reference_gently(&oid, 1);
+	commit = lookup_commit_reference_gently(the_repository, &oid, 1);
 	if (commit) {
 		commit_sha1 = commit->object.oid.hash;
 		archive_time = commit->date;