Bundle the DTDs, as extracted from jetty-schemas-3.1.jar
These were in lib/jsp/javax.servlet.jsp-2.2.0.v201112011158.jar in Jetty 8
but are not in any lib/jsp/*.jar in Jetty 9.
  GPL v2:
  Copyright 2003-2009 Sun Microsystems, Inc. All rights reserved.
  Copyright 2004 The Apache Software Foundation
  Copyright (c) 2009-2013 Oracle and/or its affiliates. All rights reserved.