function rel_external_and_download() {
	var links = document.getElementsByTagName("a");
	for (var i=0; i<links.length; i++) {
	   var link = links[i];
	   if (link.getAttribute("href") && link.getAttribute("rel") == "external") link.target = "_blank";
		if (link.getAttribute("href") && link.getAttribute("rel") == "download") link.target = "_blank";
	}
}

window.onload = rel_external_and_download;