The Users module uses two content variables.

Name: login_box
Tag : USERS_LOGIN_BOX
---------------------
Contains the log-in form. After logging in, it contains a small menu
of links. The admin has the option of changing the layout of the form:
vertical or horizontal. 


Name: permissions
Tag : USERS_PERMISSIONS
-----------------------
If the admin has their javascript disabled, the User module displays
the permission admin panel in this space. Best left in DEFAULT.
