Added replace unit tests.

git-svn-id: svn://graphite/diminuto/trunk@566 5dfbf39a-1452-0410-8a97-9e58fedde8e3
Store unit test passes.
Still need to comment store and tree header files.

git-svn-id: svn://graphite/diminuto/trunk@567 5dfbf39a-1452-0410-8a97-9e58fedde8e3
First cut at Cygwin port (incomplete and mostly untested).

git-svn-id: svn://graphite/diminuto/trunk@568 5dfbf39a-1452-0410-8a97-9e58fedde8e3
Decided to treat tree more like a base class in store.

git-svn-id: svn://graphite/diminuto/trunk@569 5dfbf39a-1452-0410-8a97-9e58fedde8e3