Simpler Admin Session Length Control

for osCommerce Online Merchant v2.2

I helped work on another admin session length contribution and I realized it could be so much simpler. This version requires you to have sql based admin sessions. Defaults to a minimum of 10 minutes so you can't accidentally lock yourself out of the admin. Requires only 1 row added to your database configuration table. And requires only 1 php file to be edited. It still get's the job done without editing a whole bunch of lines of code.