Once I have a patch that I'm modestly confident in, I'll write automated tests to go with it.

The tests will (at minimum):

- Create a tweaked copy of pyconfig.h that uses the opposite Unicode settings (UCS4 v UCS2)

- Build an extension module in Unicode-agnostic mode
- Make sure it loads and works

- Build an extension module in Unicode-sensitive mode
- Make sure it doesn't load