Remove dependency on Sun specific JVM classes

I found this:

[/home/opalka][/home/opalka/svn/jbossws/stack/native/trunk]>grep -r "org\.apache\.x" * | grep -v "\.svn" | grep com.sun.
modules/testsuite/native-tests/src/test/java/org/jboss/test/ws/jaxws/samples/news/Agency.java:import com.sun.org.apache.xerces.internal.jaxp.datatype.XMLGregorianCalendarImpl;
modules/testsuite/native-tests/src/test/java/org/jboss/test/ws/jaxws/samples/news/Printer.java:import com.sun.org.apache.xerces.internal.jaxp.datatype.XMLGregorianCalendarImpl;
modules/testsuite/native-tests/src/test/java/org/jboss/test/ws/jaxws/samples/dar/ReplyConverter.java:import com.sun.org.apache.xerces.internal.jaxp.datatype.XMLGregorianCalendarImpl;
modules/testsuite/native-tests/src/test/java/org/jboss/test/ws/jaxws/samples/dar/ClientHelper.java:import com.sun.org.apache.xerces.internal.jaxp.datatype.XMLGregorianCalendarImpl;

IOW our tests are dependent on Sun JVM specific classes and so these tests are not portable across different JVMs. This should be fixed.