parse.y: fix inconsistency with literals

* parse.y (rb_id_attrset): fix inconsistency with literals, allow
  ID_ATTRSET and return it itself, but ID_JUNK cannot make ID_ATTRSET.
  and raise a NameError instead of rb_bug() for invalid argument.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43083 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
ChangeLog: remove duplicated entry

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43084 b2dd03c8-39d4-4d8f-98ff-823fe69b080e