v4.0.1

What's new in Tornado 4.0.1
===========================

Aug 12, 2014
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* The build will now fall back to pure-python mode if the C extension
  fails to build for any reason (previously it would fall back for some
  errors but not others).
* `.IOLoop.call_at` and `.IOLoop.call_later` now always return
  a timeout handle for use with `.IOLoop.remove_timeout`.
* If any callback of a `.PeriodicCallback` or `.IOStream` returns a
  `.Future`, any error raised in that future will now be logged
  (similar to the behavior of `.IOLoop.add_callback`).
* Fixed an exception in client-side websocket connections when the
  connection is closed.
* ``simple_httpclient`` once again correctly handles 204 status
  codes with no content-length header.
* Fixed a regression in ``simple_httpclient`` that would result in
  timeouts for certain kinds of errors.