add some verification against MATLAB output

Add a new test which checks that the output from the Python code matches that
of MATLAB to within machine precision.

We also need a nasty workaround for Python 2/3 incompatibility with npz. The
npz format uses pickle to store objects. The pickle format is incompatible
between PYthon 2 and 3 due to Unicode encoding issues. We work around this by
ensuring that we only store plain ol'arrays in the npz file. It's mucky, but
compatible.