On a sidenote: The comment of SystemChangeNotification-Tests-gk.11
says "I am not sure why we are sending a class category along when we
change a class comment?"

This bugs me also. It's not clear to me, why we are sending in the
category at these methods of SystemChangeNotifier:
  classAdded: inCategory:
  classCommented: inCategory:
  classRemoved: fromCategory:
  classRenamed: from: to: inCategory:
I would think that in all these places the class category is the same
as the category passed in the parameter.

Balázs