gen_del(): Looks like much this was copy/pasted from
slot_tp_del(), but while the latter had to cater to types
that don't participate in GC, we know that generators do.
That allows strengthing an assert().
diff --git a/Objects/genobject.c b/Objects/genobject.c
index a00aa85..15e53dd 100644
--- a/Objects/genobject.c
+++ b/Objects/genobject.c
@@ -185,7 +185,7 @@
_Py_NewReference(self);
self->ob_refcnt = refcnt;
}
- assert(!PyType_IS_GC(self->ob_type) ||
+ assert(PyType_IS_GC(self->ob_type) &&
_Py_AS_GC(self)->gc.gc_refs != _PyGC_REFS_UNTRACKED);
/* If Py_REF_DEBUG, _Py_NewReference bumped _Py_RefTotal, so