Fix for issue #14 (Windows support on CPython 3.3)

I bumped into CPython 3.3 issue #16283 on Win64 today.  This patch is a workaround until CPython can be fixed, and addresses pyusb issue #14.  

I've tested with libusb0 on Windows 7 64-bit, CPython 3.3 64-bit and 2.7.3. Unfortunately I don't have time to setup openusb/libusb1 on Windows right now.  

Thanks for all the great work you've done with pyusb; I've used it extensively at work.