Fix weakrefs to sets

src/runtime/set.cpp

@@ -877,6 +877,8 @@ using namespace pyston::set;
 void BoxedSet::dealloc(Box* _o) noexcept {
     BoxedSet* o = (BoxedSet*)_o;
 
+    PyObject_ClearWeakRefs(o);
+
     PyObject_GC_UnTrack(o);
     for (auto p : o->s) {
         Py_DECREF(p.value);

src/runtime/types.cpp

@@ -3883,6 +3883,7 @@ void BoxedClass::dealloc(Box* b) noexcept {
     if (PyObject_IS_GC(type))
         _PyObject_GC_UNTRACK(type);
 
+    // We can for the most part avoid this, but I think it's best not to:
     PyObject_ClearWeakRefs((PyObject*)type);
 
     type->clearAttrsForDealloc();

test/tests/weakrefs.py

-# expected: reffail
 import weakref
 import array
 import re