bit.  For one, this class:

    class C(object):
        def __new__(myclass, ...): ...

would have no way to call the __new__ method of its base class, and
the workaround (to create an intermediate base class whose __new__ you
can call) is ugly.

So, I've come up with a better solution that restores object.__new__,
but still solves the original problem, which is that built-in and
extension types shouldn't inherit object.__new__.  The solution is
simple: only "heap types" inherit tp_new.  Simpler, less code,
perfect!