behavior.  [ruby-dev:32192]

* encoding.c (enc_name): Encoding should not rely on ENCODING in
  the FL_USERS flags.

* encoding.c (rb_enc_from_encoding): do not call rb_enc_associate
  for encoding itself.

* encoding.c (enc_register_at): ditto.

* marshal.c (r_ivar): do not set real instance variable for
  encoding data associated.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@13848 b2dd03c8-39d4-4d8f-98ff-823fe69b080e