Optimization: When trying to determine the current page, call admin_url() only once instead of for each item. However, call it for each item if "admin_url" is filtered because another plugin could change the URL depending on the menu item.

git-svn-id: https://plugins.svn.wordpress.org/admin-menu-editor/trunk@795957 b8457f37-d9ea-0310-8a92-e5e31aec5664