Code review comment for lp:~txamqpteam/txamqp/support-basic-return

This is work done with Esteve to add support for the AMQP basic return message. It adds a mandatory argument to outgoing messages, resulting in a basic return if the message is not routable.

There is an outstanding issue with what, if anything, to do with Thrift oneway methods. They have no client side deferred whose errback can be called if they are unroutable.