Much tinkering with the test suite - sdot now passes!

-Test suite expects dot to return value, not be a void fcn - changed.

-Test suite was failing for negative incrememnts - changed dot so that
if increment is -ve, we start at the end of the vector (standard BLAS
proceedure, I think).

-sblat1mod.f contains many comments that make the test suite easier to
comprehend. Possibility that such tinkering added bugs, so use sblat1
for actual testing.