parse-opts: prepare for OPT_FILENAME

To give OPT_FILENAME the prefix, we pass the prefix to parse_options()
which passes the prefix to parse_options_start() which sets the prefix
member of parse_opts_ctx accordingly. If there isn't a prefix in the
calling context, passing NULL will suffice.

Signed-off-by: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

archive.c

@@ -309,7 +309,7 @@ static int parse_archive_args(int argc, const char **argv,
 		OPT_END()
 	};
 
-	argc = parse_options(argc, argv, opts, archive_usage, 0);
+	argc = parse_options(argc, argv, NULL, opts, archive_usage, 0);
 
 	if (remote)
 		die("Unexpected option --remote");