Hold the boat

This one is painful. I did not write good enough tests, and so the shutdown behavior I thought was working did not. There is somewhat of a race condition here where if the worker were writing to gearman we would wait, but ultimately this is just a big fail on my part:

![image](https://cloud.githubusercontent.com/assets/603357/4228195/688703b0-3956-11e4-9078-800647a45f76.png)

![screenshot 2014-09-10 18 53 37](https://cloud.githubusercontent.com/assets/603357/4228202/81a764a2-3956-11e4-9eaf-be8b22557ccb.png)


Is there a reason for the change from the argument being a function wrapped in a function to just a function? Also, is it possible for this cb to get called more than once? If that is part of your intention can you document a bit?