The method was removed from Rails 3 RC 1, though it appears it will be
included in the final release. See:

Removed:
http://github.com/rails/rails/commit/b0b9bf320409b66c6c6b680371aca590297cd4cc

Reinstated:
http://github.com/rails/rails/commit/88b5f938cf7d3eb26ad204451a4dbb9c2cf4f571