No way to shut down the Listener

[jfmesse]

Occasionally processes need to be restarted, but the Listener class appears to expose no way of cleanly shutting down. Forcibly shutting down introduces a risk of losing messages that are still being processed by the client, but have been ack-ed by the listener immediately after entering the onMessage function.

Having better control of ack-ing would help, but having say a shutdown method on the Listener that could be called after an appropriate signal has been received would be ideal.

[zakagan]

I'll take a look at this as well