Deactivatable for Rails 3.1

Changed all queries to ActiveRelation object. 
Refactored some of the code used to remove the 'deactivated_at' scopes, due to internal changes made in Rails 3.1.
Added 'status' field on the DeactivatableDependency class in order to test chained scope queries.
Changed the test_db adapter information, and added a line which removes the existing db before the tests are run, in order to prevent db errors.
Bumped version.