This filter assumes the response generated by the
server (Struts Action, servlet, JSP, whatever) is
XML, and transforms it via XSLT. Configuration:
* pathSpec, pathList - The usual
* xsltPath - Context-relative path to XSLT stylesheets
* xsltMappings - A CSV list of name/value pairs where
the name is a request path (with wildcard support)
and the value is the XSLT to process it with.