Prevent hanging of requests for schema dependencies

[jakzal]

I think this has proved we should discourage (or make it impossible) for end users to use completesEventually() with completes() directly:

CompletesEventually completes = completesEventually();
eventualOutcome.andFinallyConsume((R value) -> completes.with(value));
return completes();

and suggest using answerFrom() instead:

return answerFrom(eventualOutcome);

Related PRs:

• https://github.com/vlingo/xoom-common/pull/44
• https://github.com/vlingo/xoom-actors/pull/91