Specify Ruby, bundler & rake versions; Mongoid 3 requires Ruby 1.9.3

After some researching into MongoDB, looking at (on Heroku) config/database.yml, and necessarily (per Gemfile) slowly installing libv8 and therubyracer on my (Debian) local box, the resolution...

turned out to be (the best practice of) specifying Ruby, Bundler, and Rake versions in the Gemfile.

Heroku's default was Ruby 1.9.2; that's why we got mysterious ORM messages (I believe).

The app is past the 'failed' stage now, on my Heroku instance:

http://guarded-bastion-7857.herokuapp.com/

BTW, my instance works even after I removed the (default) Heroku add-on, 'Heroku Postgres Dev'.