function add_timing_point($description = '')
 {
     if (!debug::is_debug_enabled()) {
         return;
     }
     if (!debug::show_message(DEBUG_SHOW_TIMING_POINT)) {
         return;
     }
     $debug =& debug::instance();
     $time = microtime();
     $tp = array('time' => $time, 'description' => $description);
     $debug->time_points[] = $tp;
     $debug->write(DEBUG_TIMING_POINT, $description);
 }