Use setuptools to build libuv, and enable it on Windows (especially for PyPy)

Let PyPy fail on Appveyor for now. Also bump Travis PyPy to 5.9.0 because I can't reproduce the test__makefile_ref failure locally on 5.9.0. Fixes #1029.

Successful test with CPython 3.5 on Windows 10; have to elide getaddrinfo and getnameinfo because they won't link.

Tweak test for random ImportWarning from Python 3: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__

Use setuptools to build libuv. This should be much simpler, especially on windows, at the cost of manually keeping up with link arguments and file deps.

Initial libuv support

Hmm, the 32-bit builds all failed with 'The system cannot find the drive specified.' five times. Maybe it didn't like our comments?

This requires some changes to the way we handle errors, specifically
for signals in the monkey-patched test_selectors.py and
test_socket.py.

It's not absolutely clear that this is the right thing to do in all
cases.