Made progress with the reconnect tests.  The simple ones now work.
The trick was to call asyncore.poll() until the client is
(dis)connected before going to the next phase of the test; I added
pollUp() and pollDown() helper methods for this purpose.

The reconnect "upgrade" test doesn't work yet.  That is, a client is
created in fallback mode, initially connecting to a read-only server.
So far so good.  Then the server is shut down.  Somehow an attempt to
store once the server is down simply *hangs*.

No progress with the multiple server fallback test.