add spec to ensure that decorators work with delegation

spec/draper/decorator_spec.rb

@@ -357,6 +357,10 @@ describe Draper::Decorator do
       Array(subject).should be_a Array
     end
 
+    it "proxies delegated methods" do
+      subject.delegated_method.should == "Yay, delegation"
+    end
+
     context "with method security" do
       it "respects allows" do
         source.stub(:hello_world, :goodnight_moon).and_return(:proxied)

spec/support/models/product.rb

@@ -1,6 +1,8 @@
 class Product < ActiveRecord::Base
   include Draper::Decoratable
 
+  delegate :delegated_method, to: :thing
+
   def self.find_by_name(name)
     @@dummy ||= Product.new
   end

spec/support/models/some_thing.rb

@@ -1,2 +1,5 @@
 class SomeThing < Product
+  def delegated_method
+    'Yay, delegation'
+  end
 end