Timeout-Access header always contains incorrect value "<function1>"

**Issue by [nartamonov](https://github.com/nartamonov)**
_Tuesday Mar 22, 2016 at 16:00 GMT_
_Originally opened as https://github.com/akka/akka/issues/20120_

---

Following path returns response "Timeout-Access = ":

``` scala
path("test") {
get {
optionalHeaderValueByName("Timeout-Access") { timeout =>
complete(s"Timeout-Access = ${timeout.get}")
}
}
}
```

It's because [`TimeoutAccessImpl`](https://github.com/akka/akka/blob/master/akka-http-core/src/main/scala/akka/http/impl/engine/server/HttpServerBluePrint.scala#L309) does not override `toString` which inherited by default from `scala.Function1`.

Start in akka-http-core/src/main/scala/akka/http/impl/engine/server/HttpServerBluePrint.scala around TimeoutAccessImpl and reproduce the optionalHeaderValueByName example from the issue. Verify that the Timeout-Access response no longer renders as and add or update a focused regression test if the surrounding test location is identified.

Written by the indexing model from the issue text.