Collecting ProductVersions of several servers.

FutureCrawlMain.scala

  val uris = Seq(
    "spray.io", "www.wikipedia.org"
  //TODO Works well with only 2 URIs, sometimes also with 3 URIs, but does not scale to e.g. 5 URIs!
//    , "scala-lang.org"
//    , "doc.akka.io", "public.beuth-hochschule.de/~knabe/", "fb6.beuth-hochschule.de", "stackoverflow.com/questions/tagged/scala"
//   , "esperanto.de", "tatoeba.org"
  )
  //The futures are constructed immediately one after another and are then running.
  val futures = uris.map(requestProductVersion)

  //Collect the results of all requests:
  val result = Future.sequence(futures)