Fix T::U loading.

The constants changed and there's no file on 3.0

lib/draper/test/test_unit_integration.rb

@@ -1,8 +1,17 @@
 require "rake/testtask"
-require "rails/test_unit/sub_test_task"
+
+klass = nil
+
+if Rails.version[0,3] == "3.0"
+  require 'rails/test_unit/railtie'
+  klass = Rake::TestTask
+else 
+  require "rails/test_unit/sub_test_task"
+  klass = Rails::SubTestTask
+end
 
 namespace :test do
-  Rails::SubTestTask.new(:decorators => "test:prepare") do |t|
+  klass.new(:decorators => "test:prepare") do |t|
     t.libs << "test"
     t.pattern = "test/decorators/**/*_test.rb"
   end