* vm_insnhelper.c (vm_getivar): use class sequence to check class
  identity, instead of pointer + vm state

* vm_insnhelper.c (vm_setivar): ditto

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42841 b2dd03c8-39d4-4d8f-98ff-823fe69b080e