Begin trying to install on Travis.

That breaks several of the subprocess tests.

Catch greenlet.error when destroying a hub from another thread.

Also some test tweaks for OSX on Ci.

Fixes #1631

Fixes #1626

Update c-ares to 1.16.1

Makefile patch doesn't apply, will create a new one.

Update to libuv 1.38

This has new enough kernel headers that libev builds the io_uring
backend, but testing it fails:

  ======================================================================
220  ERROR: test_linux_iouring_0 (gevent.tests.test__close_backend_fd.Test)
221  ----------------------------------------------------------------------
222  Traceback (most recent call last):
223    File "/home/travis/.runtimes/snakepit/2.7.d/lib/python2.7/site-packages/gevent/tests/test__close_backend_fd.py", line 77, in test
224      self._check_backend(backend)
225    File "/home/travis/.runtimes/snakepit/2.7.d/lib/python2.7/site-packages/gevent/tests/test__close_backend_fd.py", line 45, in _check_backend
226      hub = Hub(backend, default=False)
227    File "/home/travis/.runtimes/snakepit/2.7.d/lib/python2.7/site-packages/gevent/hub.py", line 441, in __init__
228      self.loop = self.loop_class(flags=loop, default=default) # pylint:disable=not-callable
229    File "src/gevent/libev/corecext.pyx", line 444, in gevent.libev.corecext.loop.__cinit__
230      raise SystemError("ev_loop_new(%s) failed" % (c_flags, ))
231  SystemError: ev_loop_new(50331776) failed

There are also different SSL errors (of course) on different versions.
gevent.tests.test__makefile_ref.TestSSL commonly fails to find
expected open files on most versions, and some versions don't see the
cipher suites they expect, etc.

https://ci.appveyor.com/project/denik/gevent/builds/33014124/job/lug3fye0ko2gbe7q

checking whether make supports nested variables... (cached) yes
1067./configure: line 12686: syntax error near unexpected token AX_PTHREAD('

https://travis-ci.org/github/gevent/gevent/jobs/689397295

Make zope.interface/event and setuptools required dependencies.

Fixes #1619

Update to Cython 3.0a5. Fixes #1599

Fix issue 1437 by detecting cross-thread lock usage and using an async watcher