prevent restlet resources from sending duplicate Date and Server headers

When a Nexus Restlet resource is requested ( service/local/* ), restlet sends back duplicate Date and Server headers.

There should be only one Date header, and Jetty provides this for all responses:

http://download.eclipse.org/jetty/stable-8/xref/org/eclipse/jetty/http/HttpGenerator.html#482

There should only be one Server header, with each product/version joined in the header value by a single space.

http://pretty-rfc.herokuapp.com/RFC2616#header.server
http://pretty-rfc.herokuapp.com/RFC2616#product.tokens

< HTTP/1.1 200 OK
< Date: Sat, 03 Jan 2015 16:16:33 GMT
< Server: Nexus/2.11.1-01
< X-Frame-Options: SAMEORIGIN
< X-Content-Type-Options: nosniff
< Set-Cookie: JSESSIONID=2f781ca7-d955-45c7-99e4-a84cdcfa6d4a; Path=/nexus; HttpOnly
< Set-Cookie: rememberMe=deleteMe; Path=/nexus; Max-Age=0; Expires=Fri, 02-Jan-2015 16:16:33 GMT
< Content-Type: application/xml; charset=UTF-8
< Date: Sat, 03 Jan 2015 16:16:33 GMT
< Vary: Accept-Charset, Accept-Encoding, Accept-Language, Accept
< Server: Noelios-Restlet-Engine/1.1.6-SONATYPE-5348-V8
< Content-Length: 10320