many types were subclassable but had a xxx_dealloc function that
called PyObject_DEL(self) directly instead of deferring to
self->ob_type->tp_free(self).  It is permissible to set tp_free in the
type object directly to _PyObject_Del, for non-GC types, or to
_PyObject_GC_Del, for GC types.  Still, PyObject_DEL was a tad faster,
so I'm fearing that our pystone rating is going down again.  I'm not
sure if doing something like

void xxx_dealloc(PyObject *self)
{
	if (PyXxxCheckExact(self))
		PyObject_DEL(self);
	else
		self->ob_type->tp_free(self);
}

is any faster than always calling the else branch, so I haven't
attempted that -- however those types whose own dealloc is fancier
(int, float, unicode) do use this pattern.