ActiveRecord::Relation#except and #only loses scope extensions

Given a scope with extensions
When I use the except to remove a part from the relation
Then the extensions are gone, because except returns a brand new relation object.

This means the following doesn't work (when using Kaminari, which uses extensions):

Post.page(2).except(:order).current_page

Because the current_page method was added by the page scope.

This issue is present in at least 3.0.5 and master.

The supplied patch will apply the extensions again after using except and only.

There is some duplication going on in both methods. A private method could certainly be extracted (although I'm clueless on a name).

Edit: GitHub pull request started working again: https://github.com/rails/rails/pull/231