* error.c, file.c, gc.c, hash.c, thread.c, variable.c, vm_eval.c, bin/erb:
  $SAFE=4 is obsolete.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42608 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* error.c, object.c, ext/readline/README.ja: [DOC] $SAFE=4 is obsolete.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42609 b2dd03c8-39d4-4d8f-98ff-823fe69b080e