database_pdo.php

I don't know why the pull request still thinks there's a difference between my database_mysql.php and the one in your master trunk; I pulled down a most recent copy with curl, it's supposed to be an exact match.

You said only add database_pdo.php.  I did fix a bug in html.php (a duration of '-1' sometimes means 'forever' not 'sooner than now'), and added some more mysql-for-dummies to the README.