Unidoc fails to compile implicit conversions in scaladsl Rejections

**Issue by [johanandren](https://github.com/johanandren)**
_Monday May 16, 2016 at 14:08 GMT_
_Originally opened as https://github.com/akka/akka/issues/20533_

---

Got this from unidoc when trying to release 2.4.5:

```
[error] /Users/johan/Code/Lightbend/Akka/master/akka-http/src/main/scala/akka/http/scaladsl/server/Rejection.scala:253: value asScala is not a member of akka.http.javadsl.server.Rejection
[error] transform(Util.immutableSeq(t).map(x ⇒ x.asScala)).map(_.asJava).asJava // TODO "asJavaDeep" and optimise?
[error]
```

File compiles fine with just scalac from sbt (also clean + compile is fine).

Applied workaround in #20532 that hopefully can be reverted when someone figures this out

Start with akka-http/src/main/scala/akka/http/scaladsl/server/Rejection.scala around line 253 and reproduce the failure through Unidoc, comparing it with a normal sbt scalac compile. Review workaround #20532 and the implicit-conversion imports or scope involved; done means Unidoc compiles this code without the workaround.

Written by the indexing model from the issue text.