Add comment explaining the mouseHandled flag

Author: kborchers

ui/jquery.ui.menu.js

@@ -38,6 +38,8 @@ $.widget( "ui.menu", {
 
 	_create: function() {
 		this.activeMenu = this.element;
+		// flag used to prevent firing of the click handler
+		// as the event bubbles up through nested menus
 		this.mouseHandled = false;
 		this.element
 			.uniqueId()