* class.c, include/ruby/ruby.h: add write barriers for T_CLASS,
  T_MODULE, T_ICLASS.
* constant.h: constify rb_const_entry_t::value and file to detect
  assignment.
* variable.c, internal.h (rb_st_insert_id_and_value, rb_st_copy):
  added. update table with write barrier.
* method.h: constify some variables to detect assignment.
* object.c (init_copy): add WBs.
* variable.c: ditto.
* vm_method.c (rb_add_method): ditto.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41299 b2dd03c8-39d4-4d8f-98ff-823fe69b080e