Include ERB::Util in RhoController so that "html_escape" and its alias "h" are available by default in .erb views

Rakefile is removing erb.rb from the rhodes bundle. That leaves .erb views without any built-in way to escape potentially-unsafe HTML. I propose that

- erb.rb not be deleted
and
- RhoController includes ERB::Util by default

so that you can use <%=html_escape @value %>  and the shorthand version <%=h @value %> in all .erb views