message: add explicit onChange callback in cocoa cvSetTrackbarPos
diff: @@ -451,6 +451,9 @@ CV_IMPL void cvSetTrackbarPos(const char* trackbar_name, const char* window_name
  slider = [[window sliders] valueForKey:[NSString stringWithFormat:@"%s", trackbar_name]];
  if(slider) {
  [[slider slider] setIntValue:pos];
  + if([slider respondsToSelector:@selector(handleSlider)]) {
  + [slider performSelector:@selector(handleSlider)];
  + }
  }
  }
  [localpool5 drain];
  @@ -1187,7 +1190,7 @@ static NSSize constrainAspectRatio(NSSize base, NSSize constraint) {
  [slider setMaxValue:100];
  [slider setContinuous:YES];
  [slider setTarget:self];
  - [slider setAction:@selector(sliderChanged:)];
  + [slider setAction:@selector(handleSliderNotification:)];
  [self addSubview:slider];
  [self setAutoresizingMask:NSViewWidthSizable];
  @@ -1197,8 +1200,12 @@ static NSSize constrainAspectRatio(NSSize base, NSSize constraint) {
  return self;
  }
  -- (void)sliderChanged:(NSNotification *)notification {
  +- (void)handleSliderNotification:(NSNotification *)notification {
  (void)notification;
  + [self handleSlider];
  +}
  +
  +- (void)handleSlider {
  int pos = [slider intValue];
  NSString *temp = [self initialName];
  NSString *text = [NSString stringWithFormat:@"%@ %d", temp, pos];
  