Make menus manipulation easier for plugin developers

 * Add a wp_nav_menu_objects filter, which gets a sorted list of all menu node objects in the currently rendered menu
 * Add current, current_item_ancestor and current_item_parent boolean member variables to each menu node object, which are true when the item has the current-menu-item, current-menu-ancestor or current-menu-parent CSS class respectively


git-svn-id: https://core.svn.wordpress.org/trunk@15544 1a063a9b-81f0-0310-95a4-ce76da25c4cd