Shopify/batman — pull request #454 by TheJeff (2012-06-05 21:53:13+00:00)
Title: Set an accessor on AssociationSets so we can do data-hideif: asssociation.loaded

AssociationProxy already has this, but AssociationProxy does not. Basically allows me to do this:

```
%div{ "data-hideif" => "post.comments.loaded"} Loading
%div{ "data-foreach-comment" => "post.comments"}
.... Stuff
```