[Desktop12.04-Topic] Improved Authentication

[Robert Ancell]

It would be nice to improve the authentication mechanisms in Ubuntu to
be more user friendly and make it easier to enable modern authentication
schemes.  This will probably involve:
- Reviewing the messages/prompts in PAM for appropriateness
- Adding hints to PAM to allow GUIs to better display the prompts (i.e.
if a prompt is for a password, key number, if prompting for a password
change).
- Improving the Unity Greeter prompts to interpret the hints
- Improving PolicyKit to interpret the hints
- Making it easier to enable non-password authentication (e.g. LDAP, two
factor).