code: function appendUrl(url, urls) {
      var i = urls.length
          found = false;
      while (i--) {
          if (utils.compareUrl(urls[i], url)) 
            found = true; 
      }
      if (found === false && utils.isUrl(url)) 
        urls.push(url);
  }
docs: append a url if it is not already in the urls array