Update maint/requirements.txt versions.

Everything but autopep8, which seems to have trouble installing on py27.
Switch to python 3.4 for maint/requirements.txt.
Pyflakes cleanup.

Includes real python3 bugfixes for tornado.auth.FacebookMixin and
tornado.platform.twisted.
Bump required autopep8 version.

This version can be installed on py3 but was having problems on py2.
Autopep8 formatting updates.