Support for a default paperclip queue for DJ 3.X

Here is a proposed change to delayed_paperclip to support DJ 3.X queues.  Sadly there are few options to support a distinction between 2.x and 3.x DJ hence the definition query against the default DJ queue.  

Your thoughts on viable testing strategies would be appreciated as it would be difficult to test programmatically without the use of something like rvm to swap gem stacks.  Nonetheless I did test this code against DJ 2.0.8, 2.1.4 and 3.0.5.

Thanks
k.