Fix for missing dependency in ActionDispatch::Integration

When running cucumber features from a new rails 3 app requiring
'cucumber/rails/world' would raise:

uninitialized constant ActionDispatch::Integration::Session::Test (NameError)

Fixed by requiring 'test/unit/assertions' in action_dispatch/integration
Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

actionpack/lib/action_dispatch/testing/integration.rb

@@ -2,6 +2,7 @@
 require 'uri'
 require 'active_support/core_ext/object/singleton_class'
 require 'rack/test'
+require 'test/unit/assertions'
 
 module ActionDispatch
   module Integration #:nodoc: