Fix pyflakes issues
Install asyncio for Python 3.3
Try running tests without 3.3 and 3.4
Squashed commit of the following:

commit 23e076ebd2bfc64b79ddbf0e51c4e201c703e298
Author: Denis Bilenko <denis.bilenko@gmail.com>
Date:   Fri Apr 11 18:03:44 2014 +0200

    upgrade python on travis