Woops, forgot to actually add active_support/core_ext/file/path.rb

.gitignore

@@ -19,3 +19,4 @@ railties/tmp
 bin
 .bundle
 pkg
+*.gem
\ No newline at end of file

activesupport/lib/active_support/core_ext/file/path.rb

+class File
+  unless File.allocate.respond_to?(:to_path)
+    alias to_path path
+  end
+end
\ No newline at end of file

railties/test/application/middleware_test.rb

@@ -19,6 +19,7 @@ def setup
         "Rack::Runtime",
         "Rails::Rack::Logger",
         "ActionDispatch::ShowExceptions",
+        "Rack::Sendfile",
         "ActionDispatch::Callbacks",
         "ActionDispatch::Cookies",
         "ActionDispatch::Session::CookieStore",