[python-win32] detect file modification event

[Jim McCoy]

The only warning I would add here is that you should be aware of the
fact that your watcher thread will block waiting for a change to occur
in the directory; you cannot cancel the blocked ReadDirectoryChangesW
call using the standard pywin32 bindings. We have put together some
patches for ReadDirectoryChangesW in pywin32-204 that enable you to do
this check using an io completion event so that you do not end up
blocking on the directory you are watching.  I have been a lazy bum
and left these things sitting in a directory waiting to send off to
Mark... I guess I should pass them along.

Jim