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