Intermittent test failures on Windows with OpenBLAS and "plain" BLAS/LAPACK

Follow-up to #144 

On Windows with OpenBLAS and "plain" BLAS / LAPACK (failure with latter to be confirmed), the python-control tests fail in an unpredictable fashion, with `Windows fatal exception: code 0xc0000374`; this code indicates heap corruption.

It's possible that this bug is not caused by Slycot.