Fixes inherited_resources collection authorization

This reverts e3eab13b

I don't know what was the idea of that, but it turned out REAL bad.

`collection` sets the collection instance variable. `resource_base` is used all
over CanCan. It's also used inside `load_collection?` which is checked before
`load_collection` is called. That means we actually set the collection instance
variable through inherited_resources (without any authorization whatsoever) before trying to load it through CanCan using `accessible_by`.

    1. def load_resource
    2.  unless skip?(:load)
    3.    if load_instance?
    4.      self.resource_instance ||= load_resource_instance
    5.    elsif load_collection?
    6.      self.collection_instance ||= load_collection
    7.    end
    8.  end
    9. end

`collection_instance` is set on line 5 instead of line 6.