function externalLinks()
{
  if (!document.getElementsByTagName) return;
  var anchors = document.getElementsByTagName("a");
  for (var i=0; i<anchors.length; i++)
    if (anchors[i].getAttribute("href") && anchors[i].getAttribute("rel") == "external")
      anchors[i].target = "_blank";
}
window.onload = externalLinks;