Corrects a flaw leading to an exception while building topologies that include both:
* A foreign-key join with the result not explicitly materialized
* An operation after the join that requires source materialization
Also corrects a flaw in TopologyTestDriver leading to output records being enqueued in the wrong order under some (presumably rare) circumstances.
Reviewers: Matthias J. Sax <matthias@confluent.io>, Guozhang Wang <wangguoz@gmail.com>