Make StopIteration a sink state. This is done by clearing out the

di_dict field when the end of the list is reached.  Also make the
error ("dictionary changed size during iteration") a sticky state.

Also remove the next() method -- one is supplied automatically by
PyType_Ready() because the tp_iternext slot is set.  That's a good
thing, because the implementation given here was buggy (it never
raised StopIteration).