Include Gemfile sanity check.

Part of the reason for this not being caught earlier is due to the
gemfile being setup to not require the supporting gems by default. This
creates a few specs to help manage that.
Ensure that we actually create a spec_helper file.
Share the bundler install path.
Extract rails gem loading into shared Gemfile.

When the example app is generated it puts a Rails version that is
defined by currently installed version. This works great in most
situtations, except `master` or other edge branches. The version listed
is the current version of Rails, so they diverge.

Move how we load rails into a custom Gemfile, which we eval ourselves.
We then remove the rails version put into the gemfile and share our
custom version. Due to when `rake` and other shell processes fork, the
RAILS_VERSION environment variable is properly passed through.