Reply with something the channel is going to know how to handle.
Introduce a new return code for this case, since {new, Q} is going to mess up recovery by claiming we recovered something we didn't. Also {existing, Q} would make the channel enter an infinite loop, and {absent, Q} would return an AMQP NOT_FOUND which might be bewildering to the client if it managed to receive it. So we need a fourth possibility.
Remove the warning message, it's not very interesting. Also fix an unused variable.
cosmetic: remove unnecessary FQ call
merge bug25757 into stable