decompression: Copy and mod tornado.util.GzipDecompressor

[ci skip]
phnatomjs: Copy and use websocket.py

re: chfoo/wpull#142

websocket.py is from
tornadoweb/tornado@1c36307463b1e8affae100bf9386948e6c1b2308
backport.conf: Update for .thirdparty.tornado
requirements.txt: Set tornado>=3.1.1,<5.0
phantomjs: Don't call set_exit_callback

Avoid signal/ioloop/atexit/AttributeError problems.
app_test.py: Use coroutine version of fetch

Avoid tornado getting confused and stopping/starting the ioloop
incorrectly
backport.conf: Add websocket.py to nofix=str
Merge branch 'issue/142-tornado4' into develop
changelog: Add entry: Tornado 4.0 support.

Closes chfoo/wpull#142