CAMEL-2624 pull request

Fix for asynchronous mina2 producers and consumers.
This patch will affect current users of mina2 if they don't handle null bodies in messages. Exchanges are sent with null bodies for session created, session opened and session closed events. This allows IoHandlers to be used asynchronously on the producer side and Processors to be used for asynchronous message handing on the consumer side.
If you pull and apply the patch, I will resolve CAMEL-2624.

Regards,
Chad