/**
  * Register a version of a class.
  *
  * @access private This method is only for internal use by the library.
  *
  * @param string $generalClass Class name without version numbers, e.g. 'PluginUpdateChecker'.
  * @param string $versionedClass Actual class name, e.g. 'PluginUpdateChecker_1_2'.
  * @param string $version Version number, e.g. '1.2'.
  */
 public static function addVersion($generalClass, $versionedClass, $version)
 {
     if (!isset(self::$classVersions[$generalClass])) {
         self::$classVersions[$generalClass] = array();
     }
     self::$classVersions[$generalClass][$version] = $versionedClass;
     self::$sorted = false;
 }