MAHOUT-1493 Port Naive Bayes to Spark DSL (for comment)

Created this PR to review the patch provided by Christoph Viebig and team, Students of TU, Berlin.  It is based on Sebastian's code from before the DSL was abstracted away from Spark. 
weird. this should be just 

    import RLikeDrmOps._

(since math._ is already imported)