Modified spbenchsolver help message because it could be misunderstood
What does this implement/fix?
The help message stated that the matrix should be named MatrixName.mtx and MatrixName_b.mtx. In the case of a SPD matrix, you have to name it MatrixName_SPD.mtx. I think it was not clear enough that as a consequence, the rhs should be named MatrixName_SPD_b.mtx. I actually made the mistake when trying to use spbenchsolver.