remove unguaranteed behavior
remove unguaranteed behavior

`super` of rb_define_class_under() and rb_define_class_id_under()
should be a valid class object.  Use of 0 (not NULL) has been
deprecated and warned, and will not be guaranteed at all.

eregon/rubyspec,sgarciac/spec,wied03/rubyspec,kachick/rubyspec,nobu/rubyspec,sgarciac/spec,ruby/rubyspec,ruby/spec,nobu/rubyspec,wied03/rubyspec,ruby/rubyspec,nobu/rubyspec,eregon/rubyspec,eregon/rubyspec,ruby/spec,kachick/rubyspec,kachick/rubyspec,sgarciac/spec,ruby/spec,wied03/rubyspec