message: fix latched flag propagation to python
diff: @@ -11,7 +11,7 @@ Variable::Variable(std::string id, Expr * _type, Expr * val) {
  PyObject* Variable::toJson() const {
  PyObject * d = WithNameAndDoc::toJson();
  if (!type)
  - throw "Variable has no type";
  + throw std::runtime_error("Variable has no type");
  PyDict_SetItemString(d, "type", type->toJson());
  @@ -21,6 +21,10 @@ PyObject* Variable::toJson() const {
  Py_IncRef(Py_None);
  PyDict_SetItemString(d, "value", Py_None);
  }
  + if (latched) {
  + Py_IncRef(Py_True);
  + PyDict_SetItemString(d, "latched", Py_True);
  + }
  return d;
  }
  #endif
  