Now that we have a separate internal rails_to_json, use a separate circular reference stack instead of sticking it in the options hash

Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

Inherit TestSession from Session::AbstractStore and add indifferent access to Session::AbstractStore. 

Signed-off-by: NJoshua Peek <josh@joshpeek.com>

Signed-off-by: NJoshua Peek <josh@joshpeek.com>

Remove RewindableInput middleware since all input MUST be rewindable according to a recent change in the Rack 1.0 SPEC

Eventually commit ActionDispatch::Test::MockRequest and ActionDispatch::Test:: UploadedFile upstream.