Add template files to wordpress plugin

wp-plugin-add-template

//Template fallback
add_action("template_redirect", 'my_theme_redirect');

function my_theme_redirect() {
    global $wp;
    $plugindir = dirname( __FILE__ );
    //A Specific Custom Post Type
    if ($wp->query_vars["post_type"] == 'product') {
        $templatefilename = 'single-product.php';
    //A Custom Taxonomy Page
    } elseif ($wp->query_vars["taxonomy"] == 'product_categories') {
        $templatefilename = 'taxonomy-product_categories.php';
    //A Simple Page
    } elseif ($wp->query_vars["pagename"] == 'somepagename') {
        $templatefilename = 'page-somepagename.php';
    }

    //First, see if the template is in the theme. If not, use the theme in the plugin directory
    if (file_exists(TEMPLATEPATH . '/' . $templatefilename)) {
        $return_template = TEMPLATEPATH . '/' . $templatefilename;
    } else {
        $return_template = $plugindir . '/themefiles/' . $templatefilename;
    }
    do_theme_redirect($return_template);
}

function do_theme_redirect($url) {
    global $post, $wp_query;
    if (have_posts()) {
        include($url);
        die();
    } else {
        $wp_query->is_404 = true;
    }
}