Completely get rid of PyClass and PyInstance.

(classobject.[ch] aren't empty yet because they also define PyMethod.)
This breaks lots of stuff, notably cPickle. But it's a step in the right
direction. I'll clean it up later.
(Also a few unrelated changes, e.g. T_NONE to define a "struct member"
that is always None, and simplification of __hash__ -- these are unfinished.)

Objects/dictobject.c

@@ -2006,13 +2006,6 @@ dict_init(PyObject *self, PyObject *args, PyObject *kwds)
 	return dict_update_common(self, args, kwds, "dict");
 }
 
-static long
-dict_nohash(PyObject *self)
-{
-	PyErr_SetString(PyExc_TypeError, "dict objects are unhashable");
-	return -1;
-}
-
 static PyObject *
 dict_iter(dictobject *dict)
 {
@@ -2045,7 +2038,7 @@ PyTypeObject PyDict_Type = {
 	0,					/* tp_as_number */
 	&dict_as_sequence,			/* tp_as_sequence */
 	&dict_as_mapping,			/* tp_as_mapping */
-	dict_nohash,				/* tp_hash */
+	0,					/* tp_hash */
 	0,					/* tp_call */
 	0,					/* tp_str */
 	PyObject_GenericGetAttr,		/* tp_getattro */