bot_seen.module: Provide the seen command

Code is in my sandbox:
http://cvs.drupal.org/viewcvs/drupal/contributions/sandbox/frando/bot_seen/

Just activate it. From then on it will remember the last message of everyone, and spit it out when asking "seen foo?".

The Regex for matching reacts to quite a few possibilities, but not to any sentence containing the word seen.