[Python-3000] PyUnicodeObject implementation

[Stefan Behnel]

Antoine Pitrou wrote:
> Also note that Marc-André Lemburg (one of the authors of the unicode
> implementation) is opposed to that change. See the discussion in the bug tracker
> issue for the details.

>From a Cython perspective, I find the lack of efficient subclassing after such
a change particularly striking. That seriously bit me in Py2 when I tried
making XML text content a bit more intelligent in lxml (i.e. make it remember
what XML element it originated from). Having the same problem for unicode in
Py3 doesn't sound like a good idea to me.

Stefan