code: function _makeVirtualFunction(methodName, tree, base, extension, extName){
  	// $.ui.fancytree.debug("_makeVirtualFunction", methodName, tree, base, extension, extName);
  	// if(rexTestSuper && !rexTestSuper.test(func)){
  	//     // extension.methodName() doesn't call _super(), so no wrapper required
  	//     return func;
  	// }
  	// Use an immediate function as closure
  	var proxy = (function(){
  		var prevFunc = tree[methodName],      // org. tree method or prev. proxy
  			baseFunc = extension[methodName], //
  			_local = tree.ext[extName],
  			_super = function(){
  				return prevFunc.apply(tree, arguments);
  			};
  
  		// Return the wrapper function
  		return function(){
  			var prevLocal = tree._local,
  				prevSuper = tree._super;
  			try{
  				tree._local = _local;
  				tree._super = _super;
  				return  baseFunc.apply(tree, arguments);
  			}finally{
  				tree._local = prevLocal;
  				tree._super = prevSuper;
  			}
  		};
  	})(); // end of Immediate Function
  	return proxy;
  }
docs: Return a wrapper that calls sub.methodName() and exposes
  this        : tree
  this._local : tree.ext.EXTNAME
  this._super : base.methodName()