update osCommerce 2.3.x to use mysqli

for osCommerce Online Merchant v2.3

Since the mysql functions used in osCommerce 2 are deprecated and due for removal from PHP I have updated our version to use the equivalent mysqli procedural functions instead if the mysqli class is installed. If mysqli is not available the old mysql functions will still be used. This is just a simple way of future proofing your osCommerce install. Note: Be absolutely certain that you perform install step 2a or you will not be able to log in to the admin side of your web site unless you have changed things so that sessions are stored someplace besides the database.