Support translated role names

Jose noticed that when role names are translated the filter module support breaks. This is due to how user_roles() handles the built in roles (anonymous and authenticated), it runs them through t().

Attached is a patch that moves and re-uses a function from the user.inc which loads up roles and doesn't push a subset of their names through t().

I'm not 100% sure of this, and would like another set of eyes on it.