RESTeasy failures should be treated like user exceptions

For some reason my ExceptionMapper isn't called for Failure or LoggableFailure, which means I cannot get hold of how to handle exceptions generated by RESTeasy.

Since RESTeasy can generate exceptions for invalid or missing Content-Type headers (one of many possible sources of exceptions in RESTeasy) it would be very nice to be able to handle them so I can write my custom response.