Allow messages to be retained past session deletion

[damienmckenna]

Thanks to both Drupal's session handling when logging out (https://drupal.org/node/754560), and the session-free nature of Pressflow, there are several scenarios where a user does not see the message being saved by core:

• User deletes their user account (via user_delete module).
• User requests their password be reset.

Pressflow should extend core to provide logic that allows these user messages to be displayed.

[pwolanin]

How does this work in Drupal 7? I don't feel like this should be an area for a lot of new logic.