message: add groups to aggr results
diff: @@ -101,6 +101,7 @@ external_pointer<T> make_external(const string &rclass, Args &&...args) {
  vector<string> aliases;
  for (expr_extptr expr : groups_p) {
  + aggregates.push_back(expr->Copy());
  groups.push_back(expr->Copy());
  }
  