Fix #349: threaded resolver hangs due to import lock

Patch by @ajdavis. https://github.com/gevent/gevent/issues/349#issuecomment-31665013

Close #350.

Add Python 3.4 to test set. Fixes #408. Fixes #487. The build is green for PyPy, Py26 and Py34. Py27 intermittently displays a timing issue; Py33 intermittently displays a refcount "leak".

Mark test__socket_dns as FLAKY: It works locally, but under Travis (due to different DNS configuration?) the IPV6 values differ by one for several of the hosts, and Python 3 returns those values here.

Fix test__ssl and test__socket under Py3.3; mostly a bytes/unicode thing. These tests, however, now hang under Py3.4 (previously they weren't getting far enough to do so), so temporarily remove from the Travis test matrix while debugging.

PyPy 2.5.1 support improvements, and ssl 2.7.9 support. Fixes #546.

Fix the test_ssl failures for Python 2.6. Add a basic tox.ini to make it easier to locally test different environments.

Back out the changes to _ssl2.SSLSocket.__init__; with the addition of _sslgte279 they should no longer be necessary.

Fix test_ares_timeout to not require a root port. Because it is still a constant port, don't fail the test if it can't be bound, like 7960b8c3.

gevent/gevent#248 and gevent/gevent#434. Fix test__ares_host_result under PyPy the same way that test_ares_timeout is by simply ignoring it. PyPy now has 4 expected failures; CPython2.7 has one (test__socket_dns6). Includes gevent/gevent#546 with modifications for PyPy.

Fix the subprocess tests on PyPy: they fail even in a stock build, so skip the one that's a problem.

Add __all__ for _sslgte279, fixing test__all under 2.7.9. Adjust test__all and test__execmodule to not examine _sslgte279 on < 2.7.9, making them pass under earlier versions.

Fix the last test_ssl failure (test_protocol_sslv2) for CPython 2.7.8 and .9. In python Issue 20207, the SSLv2 protocol was disabled by default, and thus the test was changed to expect a failure (see https://github.com/python/cpython/commit/65f2fdce200b800bd95ac6690e9654afc37897c6).  Match that change.

The same flush calls that were needed for PyPy are needed to make CPython's test__pywsgi tests pass.

Tested under Python 2.7.8 and all the test_ssl tests pass, EXCEPT for:
-- test_algorithms. That test is disabled in the 2.7.8 sourcecode, so disable it here;
-- test_protocol_sslv2, which fails with the same EOF error as described in the last commit for 2.7.9.

Fixes several test failures under 2.7.9, notably test__pywsgi and test__ssl.
There are lots of whitespace differences in the tests due to forking for CPython
<= 2.7.8.

The complete failure list follows.

The ONLY failure in 2.7/test_ssl has this traceback; I'm not sure what the cause is yet:

  ======================================================================
  ERROR: test_protocol_sslv2 (__main__.ThreadedTests)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "test_ssl.py", line 71, in f
      return func(*args, **kwargs)
    File "test_ssl.py", line 1205, in test_protocol_sslv2
      try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_SSLv23, True)
    File "test_ssl.py", line 979, in try_protocol_combo
      chatty=False, connectionchatty=False)
    File "test_ssl.py", line 909, in server_params_test
      s.connect((HOST, server.port))
    File "/gevent/gevent/_sslgte279.py", line 546, in connect
      self._real_connect(addr, False)
    File "/gevent/gevent/_sslgte279.py", line 537, in _real_connect
      self.do_handshake()
    File "/gevent/gevent/_sslgte279.py", line 504, in do_handshake
      return self._sslobj.do_handshake()
  SSLEOFError: EOF occurred in violation of protocol (_ssl.c:581)

  ----------------------------------------------------------------------

3/123 expected failures
 - //bin/python -u -m monkey_test test_ssl.py
 - //bin/python -u test__socket_dns6.py
 - //bin/python -u -m monkey_test --Event test_ssl.py

4/123 unexpected failures
 - //bin/python -u test__all__.py
 - //bin/python -u test_ares_timeout.py
 - //bin/python -u -m monkey_test test_httpservers.py
 - //bin/python -u -m monkey_test --Event test_httpservers.py