[Python-3000] Draft PEP: Dropping PyObject_HEAD

["Martin v. Löwis"]

> It sounds like a good thing, but what is the impact?  How much code will be
> broken by this proposal?

Nearly all extension modules will be broken, as PyObject_HEAD goes away.

However, it is likely that Py3k breaks all extension modules for a lot
of other reasons, as well.

Fixing this specific breakage would be easy: Just replace PyObject_HEAD
with "PyObject ob_base;". How many modules then still break, I don't
know. I expect access to ob_type is frequent in Foo_Check() macros;
those need to be rewritten to use Py_Type(op).

Martin