Support use of protected_attributes in Rails 4...

... by checking if the class being fabricated has an attr_accessible method instead of using the gem version to determine whether protected_attributes is in use.  This supports applications that are being upgrading to Rails 4 but which choose to continue using protected_attributes (via the protected_attributes gem) rather than switching to strong parameters. I tested this with ActiveRecord and it seems to work well, but I didn't get to try it with Mongoid.