Add check for super

Super {enum}= doesnt exist when using AR store & accessors

```ruby
  class Account < ActiveRecord::Base
      store :extras, accessors: [:book_of_business], coder: JSON
      attr_accessible :book_of_business
      validates_presence_of :book_of_business
      classy_enum_attr :book_of_business
  end

  account = Account.new
  account.book_of_business = BookOfBusiness::Tech
  account.save! # => NoMethodError: undefined method `super' for <Account:....>
```