[Python-3000] Changing function-related TypeErrors

[Bill Janssen]

> > Is there anywhere else in Python where the type of an object isn't
> > checkable with isinstance()?
> 
> Yes, it's called duck typing.

And, in my opinion, it's probably worth stomping out in Py3K.  It
developed as necessary because of the original dichotomy between C
classes and Python classes in Python 1, but it's now obsolete.
Mix-ins should be used instead.

Bill