Optimization: Skip menu normalization if the menu is already normalized. This only applies if the menu format version matches exactly. Menus created by older versions of the plugin will still be normalized.

Menu format version increased to 5.1.

git-svn-id: https://plugins.svn.wordpress.org/admin-menu-editor/trunk@817542 b8457f37-d9ea-0310-8a92-e5e31aec5664