I was working on my program when I found that my code calling
will/didChangeValueForKey and whatnot was totally broken and should not
have worked, but I had tests that showed that bindings did indeed work.
I wrote this as a test. I'm not sure if what's going on here is some
apple magic, or if pyobjc is doing something I don't know about. I ran
out of time before I could write it in objc to find out, but maybe the
list will find it interesting anyway.