Adding first cut at throttle unittest.
Fixed typo in periodic.

git-svn-id: svn://graphite/diminuto/trunk@594 5dfbf39a-1452-0410-8a97-9e58fedde8e3
Successful non-trivial unit test of throttle.
Fixed typo in log function of tree.

git-svn-id: svn://graphite/diminuto/trunk@595 5dfbf39a-1452-0410-8a97-9e58fedde8e3
Expanded unit test.

git-svn-id: svn://graphite/diminuto/trunk@596 5dfbf39a-1452-0410-8a97-9e58fedde8e3