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. 
err actually nonZeroCounts doesn't work because we need to indicate column. Java verbose style might be numNonZeroColElements. I await a better suggestion. This is a vector like colSums and the Java getNumNonZeroElements is an Int and isn't reliable?

The distributed check will never catch a 0 since we iterate nonZero but it is wrong and I'll fix. The inCore? I assume you mean the MatrixOps version. I'll comment there.