Small update needed for Rails Guide: Getting Started with Rails

I just finished Section 6, Creating a Resource (posts). I viewed my
first post at http://localhost:3000/posts/1 to try out the adding
comments functionality. The page displayed with the correct content,
but with this message printed immediately after the Add a Comment
heading:

DEPRECATION WARNING: f.error_messages was removed from Rails and is
now available as a plugin. Please install it with `rails plugin
install git://github.com/rails/dynamic_form.git`. (called from block
in _app_views_posts_show_html_erb___58482907_24223368__383082239 at C:/
Users/carol/carol/Programming/rails/rails_projects/blog/app/views/
posts/show.html.erb:29)

The corresponding code for the comments section in app/views/posts/
show.html.erb is:

<%= form_for([@post, @post.comments.build]) do |f| %>
    <%= f.error_messages %>

    <div class="field">
      <%= f.label :commenter %><br />
      <%= f.text_field :commenter %>
    </div>

    <div class="field">
      <%= f.label :body %><br />
      <%= f.text_area :body %>
    </div>

    <div class="actions">
      <%= f.submit %>
    </div>
<% end %>

I have done some basic study of Rails 2 during the past few months
(but am still new to programming), so this seems like an item that
remains to be changed in updating the tutorial from Rails 2 to Rails
3.

As I said, comments can still be created, but the message might
confuse or alarm someone new to programming.

Thank you,

Carol