API changes to be done in 4.0, which break code:

• DONE: MessageDispatcher: remove MessageListener
• DONE: Merge AsyncRequestHandler and RequestHandler, OR make them 2 separate interfaces, ie. AsyncRH doesn't extend RH
• DONE: Remove @Deprecated methods, properties or classes
• NOTDONE: Remove direct access to Message in JChannel.send() methods (to prevent passing in the same message more than once)
  • Power users often want to access a message object directly, e.g. set flags or add a header, so I won't remove this method
• NOTDONE: Make RspFilter --> RspFilter<T>
  • We need to be able to handle objects of type T and Throwable, so we cannot change this to T
• DONE: ProtocolStack.findProtocol(Class<?> clazz) should return generic type <T extends Protocol>>, so no casting is needed. Requires changes to a number of methods in the same class.
• DONE: Request<T>
• DONE: RpcDispatcher: only 1 Marshaller, not separate ones for reqs and rsps
• DONE: Rsp: see https://issues.jboss.org/browse/JGRP-2011