Ensure undecorated resource type for AA:Comments

Comments form were being generated from decorated resource, it breaks
AA::Comments. This patch acts on AA::Comment.resource_type that is
being used to populate resource_type hidden input in comments' form

- Add support to ActiveSupport < 4
- Remove unneeded expectation option [ci skip]
Merge pull request #2736 from brennovich/2733-fix-comment-form-for-decorated-resources

Ensure undecorated object assign for comment's resource_type