Add test for "empty char-class" error

This error sometimes comes up when processsing a render
in a template, because the "name" of the template to render
is interpolated into a regex. If the "name" is actually a
method call or other code, then the regex comes out strange.

test/apps/rails3/app/controllers/home_controller.rb

@@ -83,6 +83,11 @@ class HomeController < ApplicationController
     redirect_to url_for(url)
   end
 
+  def test_render_a_method_call
+    @user = User.find(params['user']).name
+    render :test_render
+  end
+
   private
 
   def filter_it

test/apps/rails3/app/views/home/test_render.html.erb

 <h1>Home#test_render</h1>
 <p>Find me in app/views/home/test_render.html.erb</p>
+<%= render @user %>