Update payment guide as passed total is no longer decimal

Fixes #1145

docs/source/howto/how_to_integrate_payment.rst

@@ -84,20 +84,20 @@ For example::
     # Subclass the core Oscar view so we can customise
     class PaymentDetailsView(views.PaymentDetailsView):
 
-        def handle_payment(self, order_number, total_incl_tax, **kwargs):
+        def handle_payment(self, order_number, total, **kwargs):
             # Talk to payment gateway.  If unsuccessful/error, raise a
             # PaymentError exception which we allow to percolate up to be caught
             # and handled by the core PaymentDetailsView.
-            reference = gateway.pre_auth(order_number, total_incl_tax, kwargs['bankcard'])
+            reference = gateway.pre_auth(order_number, total.incl_tax, kwargs['bankcard'])
 
             # Payment successful! Record payment source
             source_type, __ = models.SourceType.objects.get_or_create(
                 name="SomeGateway")
             source = models.Source(
                 source_type=source_type,
-                amount_allocated=total_incl_tax,
+                amount_allocated=total.incl_tax,
                 reference=reference)
             self.add_payment_source(source)
 
             # Record payment event
-            self.add_payment_event('pre-auth', total_incl_tax)
+            self.add_payment_event('pre-auth', total.incl_tax)