Adding PostgreSQL support and taking care of a few errors

This patch adds postgreSQL support, while *hopefully* maintaining compatability for mysql. I also fixed a few errors I found in this module including

-Improper use of datatypes in db_query statements
-Use of undeclared variables that breaks this module. More specificly in the listhandler_send_mail
-replaced the undefined function _user_authenticated_id() with the correct constants

Please review this, so we can put this module back in the mix for mail solutions

Thanks

Trevor