CREFs should not be shared by methods between `using'.
[Bug #11247]
* vm_insnhelper.c (vm_cref_replace_with_duplicated_cref): ditto.
* vm.c (vm_cref_dup): should copy refinements correctly.
* eval.c: use rb_vm_cref_replace_with_duplicated_cref().
* eval_intern.h: add a decl. of
rb_vm_cref_replace_with_duplicated_cref().
* vm_eval.c (eval_string_with_cref): do not need to pass
scope's CREF because VM can find out CREF from stack frames.
* test/ruby/test_refinement.rb: add a test.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52677 b2dd03c8-39d4-4d8f-98ff-823fe69b080e