We were aiming to use stable URLs to identify resources but the URL
helpers were still using dfc-v1.7 because that was the last and
overriding path of the mounted DFC Provider engine.
Using Spring was hiding an loading error. When you start Rspec, Rails
and its engines are not loaded yet. So our way to load the spec helper
via `Rails.root` did not work when you ran specs on their own without
loading Rails with Spring first.
