AbstractHstResponseState#setDateHeader sets dates as timestamp instead of in a GMT formatted style

Date HTTP headers must be set this way (and not in timestamp):

Expires: Thu, 01 Dec 1994 16:00:00 GMT

Below is how Tomcat 6 implements the HttpServletResponse#setDateHeader method:

DateFormat dateFormat = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss zzz", Locale.US);
dateFormat.setTimeZone(TimeZone.getTimeZone("GMT"));
setHeader(name, dateFormat.format(new Date(date));