cas_authenticatable strategy always returns 401 when using FakeCAS

[jacobwalkr]

In test, RackCAS's Fake CAS always seems to redirect back to CasAuthenticatableController#new, which always returns 401, which creates a loop. It does create the session correctly but after signing in with Fake CAS, you have to manually navigate back to your app.

Is it worth checking for an existing session in CasAuthenticatableController#new before returning 401?