One Page Checkout for 2.3.1

for osCommerce Online Merchant v2.3

Credit goes to original authors. Just made some changes so that it works with 2.3.1. Released with no guarantees whatsoever. Use at your own risk, and BACKUP FIRST. This is a starting point for those wishing to use OPC with osc2.3.1. Others are also working on their versions and hopefully, we can get them merged for the best results possible. I'm sure someone will come along with something better after a while, but for now, this is a good start.