Add a new method to FlatDiscount to tell if it is already in the cart.

Add a template variable to tell if there is already one in the cart.
Modify the default template to include the thank you message and to hide
the add to cart button if this coupon is already in the cart.

lib/WebGUI/Help/Asset_FlatDiscount.pm

@@ -26,6 +26,7 @@ our $HELP = {
 			{ name => "templateId", description=>"template help" },
 			{ name => "hasAddedToCart" , required=>1 },
 			{ name => "thankYouMessage", description=>"thank you message help" },
+			{ name => "alreadyHasCoupon" },
 		],
 		related => [  
 		],