Message 381639 - Python tracker

I think operator.index() should be brought to be inline with PyNumber_Index():

- If the argument is a subclass of int then return it.
- Otherwise call type(obj).__index__(obj)
- If not an int, raise TypeError
- If not a direct int, raise a DeprecationWarning

The language reference for __index__() suggests this is the direction to go (https://docs.python.org/3/reference/datamodel.html#object.__index__).