MAHOUT-1464

MAHOUT-1464 looks ready to me but can't push it yet.

My build is broken from an unrelated mr-legacy test so I'll wait to push it until my local build passes but wanted to get this out for review if anyone cares.

I took out the epinions and movielens examples, will add them back in with the CLI driver maybe. 
you can trust getNumNonZeroElements.