Fix memory handling of NSNotificationCenter observer object

[triplef]

Fixes issue discussed in db90ab6.

[rfm]

I think that's OK, but I have just written a more efficient version I was about to commit.
Almost the same code, but caching the class in a static variable

static Class GSNotificationObserverClass = Nil;

• (void) initialize
  {
  if ([GSNotificationObserver class] == self)
  {
  GSNotificationObserverClass = self;
  }
  }
  and making the check be

  if (object_getClass(observer) == GSNotificationObserverClass)
  {
  RELEASE(observer);
  }

[triplef]

Ah nice, thank you! I’ll just wait for your commit then.