[Twisted-Python] win32 now an officially supported platform

[glyph at divmod.com]

As of r16628, 'trial twisted' on a stock win32 twisted installation will actually succeed and give you a PASSED at the end of it.

I went to a lot of trouble to get things into this state, so I would appreciate it if everyone could keep it this way.

More accurately: I will personally revert any changes that cause real failures on win32.  I say "real" failures because (as the buildbot history immediately following this commit amply shows) the win32 buildbot itself seems kind of flaky; some of this may have to do with the slave itself running a released version of Twisted, I'm not sure.  Any other buildbot enforcers / reviewers should be aware that it fails intermittently and give it a few chances to build to make sure the failure is legitimate, especially if the failure is a timeout or a buildbot disconnect.

Finally, I'd like to thank everyone who provided me with help, reviews, commentary, and test fixes to get to this state, especially jerub, exarkun, foom, and jml.

Now, let's get a new release out so we can upgrade that buildbot :).