Fixes inherited_resources collection authorization

This reverts e3eab13b86

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.

lib/cancan/inherited_resource.rb

@@ -13,7 +13,7 @@ module CanCan
     end
 
     def resource_base
-      @controller.send :collection
+      @controller.send :end_of_association_chain
     end
   end
 end

spec/cancan/inherited_resource_spec.rb

@@ -32,10 +32,10 @@ describe CanCan::InheritedResource do
     @controller.instance_variable_get(:@project).should == :project_resource
   end
 
-  it "index should load through @controller.collection" do
+  it "index should load through @controller.end_of_association_chain" do
     @params[:action] = "index"
     stub(Project).accessible_by(@ability, :index) { :projects }
-    stub(@controller).collection { Project }
+    stub(@controller).end_of_association_chain { Project }
     CanCan::InheritedResource.new(@controller).load_resource
     @controller.instance_variable_get(:@projects).should == :projects
   end