Fixed the problem and added some tests. Closes #14178

the descriptor because it may be destroyed before being used, destroyed during
the update of the dict for example.

the type MRO to avoid a crash if the MRO is changed during the lookup.

during the lookup

Python curses is not linked to libncursesw. It was a regression introduced in
Python 3.3a1.

Patch from Armin, test from me.