class.c: remove recursion

* class.c (rewrite_cref_stack): remove recursion.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42848 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-09-06

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42849 b2dd03c8-39d4-4d8f-98ff-823fe69b080e