message: Added a call to SDL_ShowSimpleMessageBox() for non-Windows platforms. Closes issue
diff: #include <Windows.h>
  #endif
  +#include "SDL.h"
  using namespace NAS2D;
  @@ -59,6 +60,8 @@ void doNonFatalErrorMessage(const std::string& title, const std::string& msg)
  {
  #if defined(WINDOWS) || defined(WIN32)
  MessageBoxA(NULL, msg.c_str(), title.c_str(), MB_OK | MB_ICONERROR | MB_TASKMODAL);
  +#else
  + SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, title.c_str(), msg.c_str(), NULL);
  #endif
  std::cout << msg << std::endl;
  