1.4/1.4.1 and 1.4.2+ compatible event special .add method

jquery.event.special.foo.add.js

$.event.special.foo = {
  
  add: function( handler, data, namespaces ) {
    
    var old_handler;
    
    function new_handler(e) {
      // customize, using data, namespaces, handler.type, etc.
      old_handler.apply( this, arguments );
    };
    
    // This may seem a little complicated, but it normalizes the special event
    // .add method between jQuery 1.4/1.4.1 and 1.4.2+
    if ( $.isFunction( handler ) ) {
      // 1.4, 1.4.1
      old_handler = handler;
      return new_handler;
    } else {
      // 1.4.2+
      data = handler.data;
      namespaces = handler.namespaces;
      old_handler = handler.handler;
      handler.handler = new_handler;
    }
  }
  
};