Really modern Fabrication support

Fabrication has changed yet further since the last commit. Not well
tested as I don't use Fabrication but I have the test suite passing
locally.
Drop support for Machinist 1

Even Machinist 2 isn't well-maintained at the moment!
Fix features for latest factory_girl
Fix features for latest Bundler

Bundler can no longer be run in a nested fashion like this without
using with_clean_env. Be explicit about which Gemfile we're working
with, just in case. Also skip installing unnecessary gems in the test
app.
cucumber-rails no longer installs paths.rb