protected static function loadPatchers()
 {
     if (self::$load_patchers) {
         return;
     }
     require __DIR__ . '/Patcher/AbstractPatcher.php';
     foreach (self::$patcher_list as $classname) {
         require __DIR__ . '/Patcher/' . $classname . '.php';
     }
     self::$load_patchers = true;
 }