Rails 4.0 is going to depend on Rack 1.5.x so let's test against Rack master
We are inside Request::Session
Session now inherits from Rack::Session::Abstract::SessionHash
Add back TestSession::DEFAULT_OPTIONS
Is NullSessionHash responsibility to know, create and use a null store
Leave Session.create responsibility to the SessionStore
Define DEFAULT_OPTIONS inside TestRequest
Delegate options to env
Point gemspec to the available beta to run the full suite