Add support for is_newer_than and is_older_than. is_older_than currently doesn't work as expected, but is_newer_than works fine.

src/librc/rc.map

@@ -13,6 +13,7 @@ global:
 	rc_environ_fd;
 	rc_find_pids;
 	rc_getline;
+	rc_newer_than;
 	rc_runlevel_exists;
 	rc_runlevel_get;
 	rc_runlevel_list;