/**
 * goto URL without losting refer
 * @see http://oldj.net/article/referrer-by-location-href-in-ie/
 */
function gotoUrl(url) {
	if (!document.attachEvent) {
		//define for none-IE browsers
		location.href = url;
	} else {
		//define for IE
		var refer_link = document.createElement("a");
		refer_link.href = url;
		document.body.appendChild(refer_link);
		refer_link.click();
	}
}