Fix Rails 3 route generation in test helper.

This allows us to add the Routes to Rails 3 without clobbering the
application routes; I missed a bug in my original commit where I assume
drawing routes which had previously been finalized caused a nil
exception in Rails 3.0 (but worked fine in later versions). I found a
solution here:

http://experiments.openhood.com/rails/rails%203/2010/07/20/add-routes-at-runtime-rails-3/

The solution is to clear the routes, reload the application routes, and
then draw the new routes for the test action. I was *so* close to have
that exact implementation previously; I wish I'd found this article
sooner. :)

One other change I made was to use `::Rails.application.routes_reloader`
rather than `::Rails::Application.routes_reloader`, which works across
Rails 3.0-4.2.