ConversionFilter wipes out POST requests making RESTlet unable to process the request body.

This is the same problem of the one presented here: http://jira.xwiki.org/jira/browse/XWIKI-3279

the doFilter method uses getParameterValues() to retrieve relevant information. This method has the side-effect of invalidating the request body by consuming its input stream, so when the request reaches the RESTlet subsystem the body is already consumed and the request appears to be empty.

This happens only for POST requests with an application/www-form-urlencoded.