function attachEventListener(target, eventType, functionRef, capture) {
    if (typeof target.addEventListener != "undefined") {
        target.addEventListener(eventType, functionRef, capture);
    } else if (typeof target.attachEvent != "undefined") {
        target.attachEvent("on" + eventType, functionRef);
    } else {
        return false;
    }
    return true;
}

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