[ Resolution proposed by ballot comment: ]

Decide whether the requirement is to block until finished or to call join, and rewrite to match.

Addresses US-205

[futures.async] p. 3: The third sentence says "If the invocation is not deferred, a call to a waiting function on an asynchronous return object that shares the associated asynchronous state created by this async call shall block until the associated thread has completed." The next sentence says "If the invocation is not deferred, the join() on the created thread..." Blocking until a thread completes is not necessarily a join.