Fix the "asynch" tutorial

The "asynch" tutorial does not work with EJB3 on JBoss-5.0 GA. It fails with the following exception:

[java] Exception in thread "main" java.lang.ClassCastException: $Proxy2
[java] at org.jboss.ejb3.asynchronous.Asynch.getAsynchronousProxy(Asynch.java:38)
[java] at org.jboss.tutorial.asynch.client.Client.main(Client.java:40)
[java] Java Result: 1

The ClassCastException arises from this line in org.jboss.ejb3.asynchronous.Asynch.getAsynchronousProxy:

JBossProxy proxy = (JBossProxy)ejbRef;

The proxies that we create in EJB3 on JBoss-5.0, no longer implement this JBossProxy interface and hence this exception.

P.S: EJB3 proxies on JBoss-4.x do implement this JBossProxy.