Update ruby version for RVM

Under 1.9.2, `bundle install` fails with the following error:

Gem::InstallError: activesupport requires Ruby version >= 1.9.3.
An error occurred while installing activesupport (4.0.0), and Bundler 
cannot continue. Make sure that `gem install activesupport -v '4.0.0'`
succeeds before bundling.
Raise exceptions on invalid step requests

The current implementation accepts the params[:id] value without 
question, which leads to the potential for vulnerabilities like #94, 
since it allows potential attackers/clever users to bypass the step 
definitions established in the controller.

This performs a strict check of the requested step against the steps 
defined for the Wicked::Wizard controller, and raises an exception if
no matching step can be identified. For the sake of friendly error-
handling (e.g., rendering 404 pages appropriately), special runtime 
error classes have been introduced.
Clean up step validation refactor

- Ensure that step setup is validated on #index calls
- DRY out setup call in Translated module
- Break apart check_steps! validations appropriately
- Pull error messages into class definitions
Merge pull request #95 from ahorner/prevent-invalid-step-requests

Raise exceptions on invalid step requests