Remove no-cache header for xml schema files

This is a followup of JBIDE-20610 . In the past we were trying to figure out how to make validation in Eclipse faster. The problem is that xml schema files return no-cache header and so Eclipse needs to fetch them over and over again.
We tried to solve this on Eclipse side - allow ignoring of the no-cache http header. But why not try to solve this properly on the server side at least where we have control over it? I think there is no reason why request to urls like http://jboss.org/j2ee/dtd/service-ref_4_0.dtd should return no-cache.