(is_pointer_to_heap): check alignment out of loop.
  (id2ref): avoid collision between symbols and objects.
  (rb_obj_id): ditto.  moved from object.c.
  [ruby-talk:178364] [ruby-core:7401]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@10015 b2dd03c8-39d4-4d8f-98ff-823fe69b080e