In Play 2.2, the Cached decorator causes Cache.set to be passed an
instance of play.api.libs.Iteratee[Array[Byte],SimpleResult]
instead of an instance of play.api.mvc.Result.  To serialize the
cached response into Redis, have to unwrap the iteratee by
running it to get its SimpleResult.
Remove support for deprecated PlainResult and AsyncResult; only wrap/unwrap
SimpleResult.  Map futures asynchronously instead of using await.