Message 309001 - Python tracker

Éric: in python3 if no .py is found but a .pyc is found where the .py is expected, it will be imported and run.  This supports sourceless package distributions, which is something we only sorta-support :)

The change looks simple enough that it might be worth doing, but I'll leave that to the unittest maintainers.  If accepted there should be comments as to why a .pyc is being checked for.