Add generic support for extensions that modify amount (eg. percentagepricesetfield and extrafee)

js/crm.payment.js

@@ -18,9 +18,13 @@
           totalAmount += parseFloat($(this).data('amount'));
         });
       }
-      else if (typeof CRM.percentagepricesetfield !== 'undefined' && typeof CRM.percentagepricesetfield.calculateTotalFee === 'function') {
-        totalAmount = CRM.percentagepricesetfield.calculateTotalFee();
-      }
+      else if (typeof calculateTotalFee == 'function') {
+          // This is ONLY triggered in the following circumstances on a CiviCRM contribution page:
+          // - With a priceset that allows a 0 amount to be selected.
+          // - When we are the ONLY payment processor configured on the page.
+          // It is ALSO replaced by percentagepricesetfield and extrafee extensions
+          totalAmount = parseFloat(calculateTotalFee());
+        }
       else if (document.getElementById('totalTaxAmount') !== null) {
         totalAmount = parseFloat(this.calculateTaxAmount());
         this.debugging(this.name, 'Calculated amount using internal calculateTaxAmount()');