Add 'current-menu-parent' class to post type menus

gistfile1.php

<?php
// Add 'current-menu-parent' CLASS TO CUSTOM POST TYPE MENUS
// make sure to add the registered custom post type to the menu 'Title Attribute'
add_filter('nav_menu_css_class', 'current_type_nav_class', 10, 2);
function current_type_nav_class($classes, $item) {
    // Get post_type for this post
    $post_type = get_query_var('post_type');

    // Go to Menus and add a menu class named: {custom-post-type}-menu-item
    // This adds a 'current_page_parent' class to the parent menu item
    if( in_array( $post_type.'-menu-item', $classes ) )
        array_push($classes, 'current_page_parent');

    return $classes;
}