TP: loopback=true does not discard multicast messages from self

In TP.handleMyMessage(), we have this code:
if(loopback && multicast && msg.isFlagSet(Message.LOOPBACK))

{ return; // drop message that was already looped back and delivered }

Because LOOPBACK is never set in Message, a multicast message sent by A will always (1) get looped back to A and (2) get received but not discarded to to the above code.

The correct code should check whether the sender and receiver are identical, e.g.
if(loopback && multicast) {
if(!isSingleton())

{ if(local_addr != null && local_addr.equals(msg.getSrc())) return; // drop message that was already looped back and delivered }

}

The added twist is that we need to handle the case where the shared transport doesn't have a local_addr. In this case, TP.ProtocolAdapter.up() needs to run the same check and discard the message if needed.