Change gem dependencies to make it work with Rails 3 and TB 3.0.0

This PR just does the minimum to make backstage work in my somewhat specific circumstances.  Hopefully, they apply to others. Oh, and I removed the bundler dependency, which is probably bad, but I need a 1.4 pre release in my current env, but didn't want to account for that here.  

In either case, I can now use backstage with 3.0.0.  Yay!