change scope to class method

lib/kaminari/models/active_record_model_extension.rb

@@ -6,14 +6,16 @@ module Kaminari
 
     included do
       self.send(:include, Kaminari::ConfigurationMethods)
+    end
 
+    module ClassMethods
       # Fetch the values at the specified page number
       #   Model.page(5)
-      self.scope Kaminari.config.page_method_name, Proc.new {|num|
-        limit(default_per_page).offset(default_per_page * ([num.to_i, 1].max - 1))
-      } do
-        include Kaminari::ActiveRecordRelationMethods
-        include Kaminari::PageScopeMethods
+      define_method(Kaminari.config.page_method_name) do |num = nil|
+        limit(default_per_page).offset(default_per_page * ([num.to_i, 1].max - 1)).extending do
+          include Kaminari::ActiveRecordRelationMethods
+          include Kaminari::PageScopeMethods
+        end
       end
     end
   end