More appveyor skips.

This time, I saw a bunch of errors like this, which maybe suggest something is
leaking between tests, but I don't know what:

  ===================================================
  ERROR: test_quit (__main__.Test)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "C:\projects\gevent\src\greentest\greentest.py", line 289, in wrap_restore_handle_error
      return method(self, *args, **kwargs)
    File "C:\projects\gevent\src\greentest\greentest.py", line 278, in wrap_error_fatal
      return method(self, *args, **kwargs)
    File "C:\projects\gevent\src\greentest\greentest.py", line 161, in wrap_timeout
      return method(self, *args, **kwargs)
    File "test__backdoor.py", line 75, in test_quit
      conn = self._create_connection()
    File "test__backdoor.py", line 46, in _create_connection
      conn.connect(('127.0.0.1', self._server.server_port))
    File "C:\Python34-x64\lib\site-packages\gevent\_socket3.py", line 291, in connect
      r = getaddrinfo(address[0], address[1], self.family)
    File "C:\Python34-x64\lib\site-packages\gevent\_socketcommon.py", line 272, in getaddrinfo
      return get_hub().resolver.getaddrinfo(host, port, family, socktype, proto, flags)
    File "C:\Python34-x64\lib\site-packages\gevent\resolver_thread.py", line 65, in getaddrinfo
      return self.pool.apply(_socket.getaddrinfo, args, kwargs)
    File "C:\Python34-x64\lib\site-packages\gevent\pool.py", line 326, in apply
      return self.spawn(func, *args, **kwds).get()
    File "C:\Python34-x64\lib\site-packages\gevent\event.py", line 382, in get
      self._wait_core(timeout, ())
    File "C:\Python34-x64\lib\site-packages\gevent\event.py", line 106, in _wait_core
      result = self.hub.switch()
    File "C:\projects\gevent\src\greentest\greentest.py", line 468, in switch
      return _original_Hub.switch(self, *args)
    File "C:\Python34-x64\lib\site-packages\gevent\hub.py", line 630, in switch
      return RawGreenlet.switch(self)
  OSError: [Errno 9] File descriptor was closed in another greenlet

  ----------------------------------------------------------------------
  Ran 6 tests in 10.319s

src/greentest/test__backdoor.py

@@ -53,6 +53,7 @@ class Test(greentest.TestCase):
         conn.close()
         self.close_on_teardown.remove(conn)
 
+    @greentest.skipOnAppVeyor("Times out")
     def test_multi(self):
         self._make_server()
 
@@ -69,7 +70,7 @@ class Test(greentest.TestCase):
 
         self.assertEqual(len(done), len(jobs), done)
 
-
+    @greentest.skipOnAppVeyor("Times out")
     def test_quit(self):
         self._make_server()
         conn = self._create_connection()
@@ -83,6 +84,7 @@ class Test(greentest.TestCase):
         read_until(conn, b'>>> ')
         self._close(conn, b'import sys; sys.exit(0)\r\n')
 
+    @greentest.skipOnAppVeyor("Times out")
     def test_banner(self):
         banner = "Welcome stranger!" # native string
         self._make_server(banner=banner)