git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@20461 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
and String#setbyte for the forward compatibility with 1.9, where
the behavior of String#[] and String#[]= have changed; based on
a patch from Shinichiro Hamaji in [ruby-dev:37247].
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@20461 b2dd03c8-39d4-4d8f-98ff-823fe69b080e