* class.c (make_metametaclass): new function. extracted from
rb_make_metaclass.
* class.c (rb_make_metaclass): uses make_metametaclass when called for a
metaclass.
* class.c (rb_singleton_class): creates a meta^(n+2)-class in
addition to a meta^(n+1)-class when called for a meta^(n)-class.
This is because the returned meta^(n+1) class must acts as an instance of
Class, metaclass of Class, ..., meta^(n+1)-class of Class,
Module, metaclass of Module, ..., meta^(n+1)-class of Module,
Object, metaclass of Object, ..., meta^(n+2)-class of Object,
BasicObject, metaclass of BasicObject, ..., meta^(n+2)-class of
and BasicObject even when Class, Module, Object or BasicObject has
not have its meta^(i)-class yet.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@20747 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
