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. 
OK, well thanks for reviewing!

I avoided the numNonZero from Java because it is an upper limit and didn't want to confuse this with that. This is the actual count. But nonZeroCounts is fine if you prefer. It does seem more descriptive.