public function _unload_zip(Validation $post, $field)
 {
     $zipfile = $post["zip_file"]["tmp_name"];
     if (false !== ($extract_path = themeroller::extract_zip_file($zipfile))) {
         $theme_name = themeroller::get_theme_name($extract_path);
         if (!empty($theme_name)) {
             Session::instance()->set("themeroller_name", $theme_name);
         } else {
             Kohana_Log::add("error", "zip file: css directory not found");
             $post->add_error($field, "invalid zipfile");
         }
     } else {
         Kohana_Log::add("error", "zip file: open failed");
         $post->add_error($field, "invalid zipfile");
     }
     if (file_exists($zipfile)) {
         unlink($zipfile);
     }
 }