This should fix some kqueue failures (the FDs were not unregistered,
which could result in spurious FDs being reported at a later time).

For the "negative FDs", all spurious events are now caught and logged
(I think it's better than silently ignoring them as it is now).
Hopefully we'll see an EV_ERROR with kev.data set to a sensible errno.

The implementation should now be more or less complete, apart from the
WSAPoll, which I'm unable to add/test.

Richard, in Tulip's WSAPoll code, it reads:

    class WindowsPollPollster(PollPollster):
        """Pollster implementation using WSAPoll.

        WSAPoll is only available on Windows Vista and later.  Python
        does not currently support WSAPoll, but there is a patch
        available at http://bugs.python.org/issue16507.
        """

Does this means that this code need the patch from issue #16507 to work?

Also, I've read something about IOCP: is this a replacement for
WSAPoll, are there plans to get it merged at some point to python (and
if yes, would the select module be a proper home for this)?