Make Rails's flash messages work across both apps
user
```ruby
# Taken from:
# https://gist.github.com/henrik/bb6732d5d4cddb5085a4

# The way the flash is stored in the session changed in a backwards-incompatible way.

if Rails::VERSION::MAJOR == 3
  module ActionDispatch
    class Flash
      def call(env)
        if (session = env["rack.session"]) && (flash = session["flash"])

          # Beginning of change!

          if flash.respond_to?(:sweep)
            flash.sweep
          else
            session.delete("flash")
          end

          # End of change!

        end

        @app.call(env)
      ensure
        session    = env["rack.session"] || {}
        flash_hash = env[KEY]

        if flash_hash
          if !flash_hash.empty? || session.key?("flash")
            session["flash"] = flash_hash
            new_hash = flash_hash.dup
          else
            new_hash = flash_hash
          end

          env[KEY] = new_hash
        end

        if session.key?("flash") && session["flash"].empty?
          session.delete("flash")
        end
      end
    end
  end
end
```
assistant