[BUG][FIX] UndefinedObject(Object)>>doesNotUnderstand: #at:ifAbsent: ( [er][et] kills class comment display in Package Pane Browser )

[ned at squeakland.org]

I'd prefer to use Hans-Martin's fix for this problem, since it doesn't
kill the display of the class comment in the Package Pane Browser (and
it touches less methods)