Message 69005 - Python tracker

I think the best is to ignore __instancecheck__ when
"cls.__instancecheck__" is returned as an unbound method. In this case,
we try "type(cls).__instancecheck__" instead.

Here is a patch along this idea.
I had to disable a test named "Evil", because in this case isinstance()
simply falls back to the original algorithm.

I don't know if this is applicable to 3.0: unbound methods don't exist
any more.