Extend Camel RabbitMQ with guaranteed delivery (basic.return)

So far camel-rabbitmq supports publisher acknowledgements to ensure that a massage was delivered to the brokers. However this does not guarantee that the message is delivered to queue (https://www.rabbitmq.com/confirms.html - 'When will messages be confirmed?').

To implement guaranteed delivery publisher acknowledgements have to be activated together with a return listener and publishing messages as mandatory.
In this case the basic.return will be returned to the publisher before the basic.nack or basic.ack. Only in this case we can be sure that the message is really delivered to the configured queue (or fails if no queue is available).

As a solution I provided a pull request on github together with integration tests.

https://github.com/apache/camel/pull/1116

Please let me know if I can provide further support/input.