Override property setter of base class in Python 3 - USE CASE

[Nagy László Zsolt]

> Yes, the get part works.  The set part is a pain, and a bit ugly:
>
>   super(B, B).foo.__set__(self, value)
>
> There is an issue for this on the tracker: 
> http://bugs.python.org/issue14965
>
Thank you Ethan!

The superprop pure Python implementation is very promising. (
http://bugs.python.org/file37546 ) I can use that instead of my
"property virtualizers" until Python built in support becomes available. :-)