设置cookie，判断用户是否为新用户

function get_cookie(Name) {
	var search = Name + "="
	var returnvalue = "";
	if (document.cookie.length > 0) {
		offset = document.cookie.indexOf(search)
		if (offset != -1) {
			// if cookie exists
			offset += search.length
				// set index of beginning of value
			end = document.cookie.indexOf(";", offset);
			// set index of end of cookie value
			if (end == -1)
				end = document.cookie.length;
			returnvalue = unescape(document.cookie.substring(offset, end))
		}
	}
	return returnvalue;
}