Expanded (by a lot) throttle unit test.
Now also tests variable block sizes, and simulates a long I/O sequence.

git-svn-id: svn://graphite/diminuto/trunk@599 5dfbf39a-1452-0410-8a97-9e58fedde8e3
First cut at (not quite working) shaper unit test.

git-svn-id: svn://graphite/diminuto/trunk@600 5dfbf39a-1452-0410-8a97-9e58fedde8e3