Fixed issue where a duplicate of a previous message that has eventually failed (due to the execution or exception limit been exceeded) is not ACKed thus preventing it being removed from the queue until the time out limit is reached.  This would also cause a sleep of 1 second until the next message (from either queue) is processed.
In RabbitMQ v >=2.7.0 this is a bigger problem as that the message will stay at the front of the queue blocking other messages, and thus the 1 second sleep will be continuously repeated until the time out limit is reached (default 10 minutes) and the message is finally removed.
Merge pull request #20 from chazsconi/master

Fixed issue with duplicate failed messages not being removed from the queue