io.c: preserve encodings

* io.c (rb_io_s_new): preserve encodings in warning messages.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47302 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
io.c: preserve encodings

* io.c (advice_arg_check): preserve encodings in warning messages.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47303 b2dd03c8-39d4-4d8f-98ff-823fe69b080e