When str.lower() is a security vulnerability in Python

I'm not exactly sure what's special about version 3.2 of Unicode, but it's special enough to get separate support in `unicodedata`. If there are others who need the 3.2 case-folding behaviour, maybe `str` should get a separate method for it? Or at least, a (probably keyword-only, because people with this use case will want it called out pretty explicitly, I imagine) parameter to `str.lower`.