message: Convert error message to exception
  Correct method name in message.
diff: @@ -30,8 +30,7 @@ void UIContainer::add(Control& control, NAS2D::Vector<int> offset)
  {
  if (std::find(mControls.begin(), mControls.end(), &control) != mControls.end())
  {
  - std::cout << "UIContainer::addControl(): Duplicate control." << std::endl;
  - return;
  + throw std::runtime_error("UIContainer::add(): Duplicate control");
  }
  if (mControls.size() > 0) { mControls.back()->hasFocus(false); }
  