[ic] Checkout button pressed twice, double charge

[tom at readyink.com]

I am working with someone who has an old catalog (it uses .txt files) with
a custom charge module.  Sometimes he has people whose card is charged
twice.  Is there any code in newer IC to prevent people pressing twice, or
going back and pressing again?  Thinking about it now, I think the best
place to put this would be in the payment module itself.
thank you,
tom