Ruby

• string.c (rb_str_sub_bang): String#sub! now raises an error when
  called on a frozen string, even if no change is made.
  See [ruby-core:23657]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@27559 b2dd03c8-39d4-4d8f-98ff-823fe69b080e