Release 4.5.3

2.7.8 is no longer available and "pypy3" is old and has
other issues.

There are many ways ipv6 can be disabled or broken (and it just
stopped working on travis-ci), so instead of checking flags like
socket.has_ipv6, attempt to actually bind to an ipv6 address.

Closes #2185

The servers used in tests are only listening for ipv4, not ipv6
(to avoid spurious firewall prompts on macos). In what is apparently
a recent macos change, connecting to `localhost` when the ipv6 port
is unbound now incurs a 200ms delay, slowing a full test run down
by a factor of 20.

bug introduced in #2225

otherwise a subsequent request on the same connection
will fail to be parsed

thanks to @eeelin for the bug report

See https://github.com/tornadoweb/tornado/pull/2008 for reasons
why this might be necessary.

See https://github.com/tornadoweb/tornado/pull/2008 for reasons why this
might be necessary.

since they come in as bytes on Python 3

Fixes #2020

Cherrypick FD_CLOEXEC change for 4.5.2

PR #1984 was based on the mistaken belief that we were already
doing this (and in python 3.4+, it's true, thanks to PEP 446). This
fixes a regression introduced in Tornado 4.5 in which autoreload would
leak file descriptors and leave client connections hanging.

Fixes #2057

log: Fix color logging detection

The previous logic would fail whenever curses is missing (which is
always true on windows, and is occasionally true on other platforms)
and colorama is installed but not initialized in this process (this is
a common occurrence for users of jupyter and ipython on windows).

Fixes #2013
Fixes #2015

fix backwards compatibility of url_concat for args=None

websocket: Fix use of render_string in websocket handlers

PR #1917 caused websocket connections to be "finished" early, which
broke the use of render_string by setting self.ui to None.

Fixes #2010

travis: fix using wrong Python version

virtualenv (or pip, or setuptools) no longer supports py32, so this
won't work until travis has pypy3 3.5 available.

Cleanups from various linters

auth: Update, doc, and test the facebook session_expires field

Mainly adds a bunch of blank lines.

This was recently broken by the move from url-encoding to json.

Closes #2001