Bugtracker should check for existing username before allowing the user to register. #108

When registering on bugs.python.org, I entered my desired username (ewong) and all the other necessary information.
I clicked on register and it sent me an email with a link.

When I clicked on the link, it brought me to the bug tracker page with a red notification stating
that "node with key 'ewong' exists".

The bugtracker should really check whether or not the entered username exists in the user list. If so, it should mention that to the registerer.