Fix for python bytes-to-utf-8  encoded string in the usernames

This fixes the  session join problem  opencoweb/coweb#236   that the >1 client has  with opencoweb+tornado==3.x, only minimally tested with tornado 2.x and tornado 3.1.1 on python 3.3.2  and   OCW 5822afaa46e3369eb6970d44563172bf7f7bf92d