Use class-slots instead of our custom 'walk class hierarchy and collect slot defs' code.
Use class-slots instead of our custom 'walk class hierarchy and collect slot defs' code.

This change should fix problems with allegro. Nathan Bird reported
this and suggested the proper solution.

darcs-hash:20060405120648-dd2a1-7465a4a5b047fc8dbed91f9b1ed4b9ec3b026ed7

luismbo/arnesi