fix dnu after special selector crash (fixes OaM DNU test #131)

Author: timfel

rsqueakvm/interpreter_bytecodes.py

@@ -372,6 +372,7 @@ def _sendSpecialSelector(self, interp, receiver, special_selector, w_args=[]):
         w_method = s_class.lookup(w_special_selector)
         if w_method is None:
             w_method = s_class.lookup(space.w_doesNotUnderstand)
+            self.push(receiver) # need to put receiver back on stack
             if w_method is None:
                 s_class = receiver.class_shadow(self.space)
                 assert isinstance(s_class, ClassShadow)