Adding rake gem to Gemfile, associated dependencies to Gemfile.lock, Rakefile with task to run all files presiding in 'lib' folder.

Changing lib/validations.rb file to catch error raised when token is nil, so rake task can continue to run. This had an unintended consequence of being able to test the error raised is the correct one.

Adding app/models/person.rb to work for 1.8 and 1.9 ActiveModel::Translation and ActiveModel::Lint::Tests, respectively.

Adding config/locales/app.pt_BR.yml to work with 1.8 ActiveModel::Translation.

Adding test/models/person_test.rb to test 1.9 ActiveModel::Lint::Tests.

TODO:

* get both 1.8 and 1.9 to configure correctly and run as expected in Rails guide.