[Twisted-Python] pywin32 -> cffi update and feedback request

[Zooko Wilcox-O'Hearn]

FYI, this would, if it were compatible with Tahoe's packaging, fix
these outstanding issues for Tahoe:

* https://tahoe-lafs.org/trac/tahoe-lafs/ticket/142# pywin32 can't be
installed automatically

* https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2028# Twisted
endpoints introduce a dependency on pywin32

Sincerely,

Zooko