"Expires:" Header should be set to the request date

[rhuss]

Currently we set the expires header to '-1' which, according to RFC 2616 is a possible way to mark content as stale;

HTTP/1.1 clients and caches MUST treat other invalid date formats,
especially including the value "0", as in the past (i.e., "already
expired").

To mark a response as "already expired," an origin server sends an
Expires date that is equal to the Date header value. (See the rules
for expiration calculations in section 13.2.4.)

This works for most clients, however Spring Rest Support seems to have a problem with this. So we should probably switch to the recommendation to set the Expire-Header to the Date of the request (or, if this value is not easily available at the place where the response is generated, at least to "0").

[rhuss]

Fixed now, setting Date: and Expires: to the same value for the AgentServlet and JVM HttpHandler.