MAHOUT-1574 - Add sparse handling to rows and columns of DiagonalMatrix
MAHOUT-1574 - Make SparseRowMatrix handle multiplication efficiently for special cases of SRM, DenseMatrix and other kinds of sparse matrices.  Speedup on the given test is at least several thousand x
MAHOUT-1574 - Add tests to demonstrate correctness and efficiency
MAHOUT-1574 - Fixed regression in argument checking.