message: highgui: don't terminate if we can't initialize GTK backend
  allow Users to handle such case
  exception will be thrown instead
diff: @@ -612,19 +612,33 @@ static std::vector< Ptr<CvWindow> > g_windows;
  CV_IMPL int cvInitSystem( int argc, char** argv )
  {
  static int wasInitialized = 0;
  + static bool hasError = false;
  // check initialization status
  if( !wasInitialized )
  {
  - gtk_init( &argc, &argv );
  + if (!gtk_init_check(&argc, &argv))
  + {
  + hasError = true;
  + wasInitialized = true;
  + CV_Error(Error::StsError, "Can't initialize GTK backend");
  + }
  +
  setlocale(LC_NUMERIC,"C");
  #ifdef HAVE_OPENGL
  - gtk_gl_init(&argc, &argv);
  + if (!gtk_gl_init_check(&argc, &argv))
  + {
  + hasError = true;
  + wasInitialized = true;
  + CV_Error(Error::StsError, "Can't initialize GTK-OpenGL backend");
  + }
  #endif
  wasInitialized = 1;
  }
  + if (hasError)
  + CV_Error(Error::StsError, "GTK backend is not available");
  return 0;
  }
  