Handle non-msgpack serializable data in Queues

Right now when someone puts a non-msgpack serializable piece of data in a Queue we get an inscrutable error message.

It would be nice to either ...

1. Raise an informative error message about the kind of data that one can put into queues
2. Automatically do something like call `client.scatter(data)` on the input and then gather it back when someone `get`s it on the receiving end.