Fixed tests on Windows.

Errors were

    ======================================================================
    FAIL: test_handler_callback_file_object (tornado.test.ioloop_test.TestIOLoop)
    The handler callback receives the same fd object it passed in.
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "C:\Users\schlaich\Documents\GitHub\typhoon\.tox\py27\lib\site-packages\tornado\testing.py", line 118, in __call__
        result = self.orig_method()
      File "C:\Users\schlaich\Documents\GitHub\typhoon\.tox\py27\lib\site-packages\tornado\test\ioloop_test.py", line 222, in test_handler_callback_file_object
        self.assertIs(fds[1], server_sock.fileno())
    AssertionError: 1696 is not 1696

    ======================================================================
    ERROR: test_import (tornado.test.netutil_test.ThreadedResolverImportTest)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "C:\Users\schlaich\Documents\GitHub\typhoon\.tox\py33\lib\site-packages\tornado\test\netutil_test.py", line 112, in test_import
        popen = Popen(command, preexec_fn=lambda: signal.alarm(TIMEOUT))
      File "c:\python33\Lib\subprocess.py", line 732, in __init__
        raise ValueError("preexec_fn is not supported on Windows "
    ValueError: preexec_fn is not supported on Windows platforms