Fixed bug in SparseMatrix.Indices() for submatrix
Fixed bug in SparseMatrix.Indices() for submatrix

When working with a sparse matrix submatrix the indices method returned
all the elements in the matrix. It should only return the elements in
the current submatrix. Now it does.

Signed-off-by: Tim Henderson <96597d1a2ce50fc967745fc8f11359736ad2bda4@gmail.com>

skelterjohn/go.matrix,rohanraja/go.matrix,jmptrader/go.matrix