error_messages was removed from Rails

Again, fix a rails beta upgrading bug...

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.

I don't see a need for the plugin, we can replace the error message code with the new scaffold like:

<% if @point.errors.any? %>

<h2><%= pluralize(@point.errors.count, "error") %> prohibited this point from being saved:</h2>
<ul>
<% @point.errors.full_messages.each do |msg| %>
  <li><%= msg %></li>
<% end %>
</ul>