* 1472 passing tests, 209 pending.

* porsagres does not support multiple portals at once, so we have to
  serialize what were previously parallel streams.
  * we bottleneck at the csv => zip output anyway so it doesn't matter.
* using the callback interface and abusing the Promise lock to create
  a backpressure mechanism.

* the error gets passed all the way out now on .begin as opposed to
  .transaction before, so it's both a nice place to handle it as well as
  a necessary error to handle or the tests crash.

* see comments in tap.js for details.