Log Message:
Update ruby-rspec-rails to 2.12.1.

### 2.12.1 / 2013-01-07
[full changelog](http://github.com/rspec/rspec-rails/compare/v2.12.0...master)

Bug fixes

* Operates correctly when ActiveRecord is only partially loaded (e.g., with
  older versions of Mongoid). (Eric Marden)
* `expect(subject).to have(...).errors_on` operates correctly for
  ActiveResource models where `valid?` does not accept an argument. (Yi Wen)
* Rails 4 support for routing specs. (Andy Lindeman)
* Rails 4 support for `ActiveRecord::Relation` and the `=~` operator matcher.
  (Andy Lindeman)
* Anonymous controllers define `_routes` to support testing of redirection
  and generation of URLs from other contexts. (Andy Lindeman)