I read it quickly.  It looks basically okay, but I have one issue to discuss right now.  Changing from the format unit 'O!' and calling "getuchar" to the format unit 'C' means a change in semantics.  The text in the exception will change.  Unfortunately, people do depend on that in real-world code.

It'd be nice if we could change those semantics; this won't ship until 3.5 so maybe it's okay.  I don't know.