wordpress 3.4 template files in subdirectories

The solution shared in this answer on StackOverflow works for me:

https://stackoverflow.com/questions/4647604/wp-use-file-in-plugin-directory-as-custom-page-template#answer-8255556

function get_book_post_type_template($single_template) {
    global $post;

    if ($post->post_type == 'books') {
        $single_template = dirname( __FILE__ ) . '/themefiles/single-books.php';
    }
    return $single_template;
}

add_filter( "single_template", "get_book_post_type_template" ) ;