message: don't dump current position on an illegal move
diff: @@ -258,8 +258,7 @@ bool MctsPlayer::PlayMove(Coord c) {
  }
  if (!root_->legal_moves[c]) {
  - std::cerr << "Move " << c << " is illegal:\n"
  - << root_->position.ToSimpleString() << std::endl;
  + std::cerr << "Move " << c << " is illegal" << std::endl;
  return false;
  }
  