Logic for mapcat and ParallelBuffer

@patrickwmcgee I've been testing the ClojurePlatform against the api_test.clj and almost all of them pass!  To test I've been copying over the tests from api_test.clj to my own test file...obviously your macro will be much better than this hacked approach.

Also, I know you have logic for mapcat as well, which I'm happy to use, I just wanted to get this stuff wired up first.


Another thought I had and what I had originally done was moved these into cascalog.clojure.operations.clj so that they could be unit tested. My hope was to test the operations with generative testing because it would be possible for pure clojure data structures.