Ignore two unchecked warnings.
Ignore two unchecked warnings.

The warnings are actually legitimate. Since `Future[T]` and
`CompletionStage[T]` are unrelated, we could have a subclass

    class C extends Future[A] with CompletionStage[B]

which would expose the unsoundness that the compiler warns about.
However, I assume that this was a known theoretical issue, and this
commit ignores the warning.

martijnhoekstra/scala,scala/scala,scala/scala,lrytz/scala,martijnhoekstra/scala,martijnhoekstra/scala,lrytz/scala,lrytz/scala,scala/scala,martijnhoekstra/scala,martijnhoekstra/scala,scala/scala,lrytz/scala,scala/scala,lrytz/scala,martijnhoekstra/scala,scala/scala,lrytz/scala