Fix online plan bug with multiple serial summers and certain no-ops

The comments summarize this one. But the take away is:

1) We need to look at even more robust tests, and try to think about what a correctness proof for the plans would look like.

2) There are still many opportunities to make storm plans with fewer bolts. We should take a look at that as we look to squeeze all the perf we can out of storm.
The Set looks really dangerous and I think I put it there because Set1 is a very (in terms of memory) Iterable. I'm afraid down-stream of this we are going to get strange effects with chaining. Let's be direct and just use Iterator here.