ActionView register_template_handler missing in 2.1 RC 1

The HAML plugin breaks on Rails 2.1 RC 1 because it attempts to register itself as a template handler, and results in error:

/Library/Ruby/Gems/1.8/gems/haml-1.8.2/lib/haml/template/plugin.rb:42: undefined method `register_template_handler' for ActionView::Base:Class (NoMethodError)

Steps to replicate: (on OS X 10.5)

1.) sudo gem install haml

2.) rails hamltest

3.) cd hamltest

4.) haml --rails .

5.) rake rails:freeze:edge

6.) script/server

If you rake:freeze:gems to Rails 2.0.2, the error does not occur.