Add missing readable/writable methods to FileObjectPosix. Fixes at least help() on a monkey-patched Python 3

Updates for gevent.os.fork/waitpid, mostly documentation, but also make it possible to switch off the waitpid behaviour and access the 'basic' fork function.

- De-dup wait_read, etc, from socket2 and socket3 and call them out as gevent extensions.
- Doc create_connection on socket2 and socket3 since its a standard interface.
- Docstrings for gethostbyname, etc.

Debugging code for RTD and util/cythonpp.py. Also, don't force /usr/bin/python, use the environment python (better for virtual envs). [skip ci]

Add space to gcc command line for 32-bit builds.

Also convert all multi-line strings into lists. This keeps indentation specific and makes it easier to comment on individual items.

Fix a PEP8 error.

Fix some Windows failures and enable AppVeyor

 C:\Python27\python.exe -u test_hub_join_timeout.py
  Traceback (most recent call last):
    File "test_hub_join_timeout.py", line 44, in <module>
      result = gevent.wait(timeout=10)
    File "C:\Python27\lib\contextlib.py", line 24, in __exit__
      self.gen.next()
    File "test_hub_join_timeout.py", line 22, in expected_time
      assert expected - fuzzy <= elapsed <= expected + fuzzy, 'Expected: %r; elapsed: %r' % (expected, elapsed)
  AssertionError: Expected: 0.1; elapsed: 0.15600013732910156

it does not exist here. Instead, manually copy all build commands into appveyor.yml.

Note, ECHO without arguments prints "ECHO is off." on Windows, so it should not be used.

all scripts are from from https://github.com/ogrisel/python-appveyor-demo

see also https://packaging.python.org/en/latest/appveyor.html

Under Windows that command actually breaks stuff, since 'echo' without arguments prints 'ECHO is off.'.

libev\ev.c(1813) : error C2059: syntax error : 'type'

 Traceback (most recent call last):
    File "C:\projects\gevent\greentest\greentest.py", line 213, in wrapped
      return method(self, *args, **kwargs)
    File "C:\projects\gevent\greentest\greentest.py", line 202, in wrapped
      return method(self, *args, **kwargs)
    File "C:\projects\gevent\greentest\greentest.py", line 88, in wrapped
      return method(self, *args, **kwargs)
    File "C:\projects\gevent\greentest\test__server.py", line 267, in test_serve_forever
      self.assertConnectionRefused()
    File "C:\projects\gevent\greentest\test__server.py", line 114, in assertConnectionRefused
      conn = self.makefile()
    File "C:\projects\gevent\greentest\test__server.py", line 86, in makefile
      sock.connect((self.server.server_host, self.server.server_port))
    File "c:\projects\gevent\gevent\_socket3.py", line 261, in connect
      raise error(result, strerror(result))
    File "c:\projects\gevent\gevent\win32util.py", line 89, in formatError
      return self.winError(errorcode)[1]
  TypeError: 'OSError' object is not subscriptable

to fix this exception:

  Traceback (most recent call last):
    File "test__local.py", line 4, in <module>
      from gevent import monkey; monkey.patch_all()
    File "c:\projects\gevent\gevent\monkey.py", line 369, in patch_all
      patch_socket(dns=dns, aggressive=aggressive)
    File "c:\projects\gevent\gevent\monkey.py", line 276, in patch_socket
      patch_module('socket', items=items)
    File "c:\projects\gevent\gevent\monkey.py", line 102, in patch_module
      patch_item(module, attr, getattr(gevent_module, attr))
  AttributeError: 'module' object has no attribute 'socketpair'

Explain the observed slowness of bench_sendall under PyPy and link to the discussion on the PyPy issue tracker. [skip ci]

Fixes #618: Be careful to avoid a recursive import under PyPy that can lead to an interpreter crash.

No additional tests needed, because the removal of try/except in
builtins.py would cause existing tests to fail if we still recursed.

As a side-effect, Timeout objects that can never expire should be
cheaper to create now.

See also https://bitbucket.org/pypy/pypy/issues/2089/crash-in-pypy-260-linux64-with-gevent-11b1

a subprocess test is flaky under pypy with GEVENT_FILE=thread; the existing command doesn't seem to quite catch that.