Give custorder batch handler a couple ways to affect adding new items

tailbone/views/custorders/orders.py

@@ -530,10 +530,19 @@ class CustomerOrderView(MasterView):
             return {'error': "Must specify a product UPC"}
 
         product = self.handler.locate_product_for_entry(
-            self.Session(), upc, product_key='upc')
+            self.Session(), upc, product_key='upc',
+            # nb. let handler know "why" we're doing this, so that it
+            # can "modify" the result accordingly, i.e. return the
+            # appropriate item when a "different" scancode is entered
+            # by the user (e.g. PLU, and/or units vs. packs)
+            variation='new_custorder')
         if not product:
             return {'error': "Product not found"}
 
+        reason = self.handler.why_not_add_product(product, batch)
+        if reason:
+            return {'error': reason}
+
         return self.info_for_product(batch, data, product)
 
     def get_product_info(self, batch, data):