A Cascading scheme for combining intermediate sequence files

A cascading scheme for SequenceFile that uses EB's `DelegateCombineFileInputFormat`. 
This will allow us to turn on split combination for all intermediate jobs in a cascading pipeline (currently we can only turn it on for initial LZO sources).
You have a comment below, but it would be nice to have some higher level notes on why this exists, and how to use it from a cascading job.