SI-7781 Improve test and add comment

The test should normalize the elided message,
not strip it. (Thanks qerub; I was frustrated
with kitteh's turnaround that night, hence
unwilling to improve once it passed.)
SI-7781 Comments to SessionTest

Also, it would be nice if code and expected results were
calculated lazily. That would allow tests with infinite
code but which terminate on various conditions.
SI-7804 Build partest.task with quick

Currently, you can build the `partest.task` target explicitly;
otherwise, it's a dependency for the test suite. But if I'm
tweaking some code, I'm not running test suite.

This commit makes quick freshen partest.task, which is not
burdensome.