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.

[#2550 state:committed]
Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

    Example: ActiveSupport::JSON.backend = "JSONGem"

  All internal Rails JSON encoding is now handled by ActiveSupport::JSON.encode().  Use of #to_json is not recommended, as it may clash with other libraries that overwrite it.  However, you can recover Rails specific functionality
  if you really want to use #to_json.

    gem 'json'
    ActiveSupport::JSON.backend = "JSONGem"

    class ActiveRecord::Base
      alias to_json rails_to_json
    end