Let mobile form declare if/how to auto-focus a field

and for mobile ordering, auto-focus the "units" field when editing a row

tailbone/views/purchasing/ordering.py

@@ -321,6 +321,12 @@ class OrderingBatchView(PurchasingBatchView):
         data['mode_title'] = self.enum.PURCHASE_BATCH_MODE[mode].capitalize()
         return self.render_to_response('create', data, mobile=True)
 
+    def configure_mobile_row_form(self, f):
+        super(OrderingBatchView, self).configure_mobile_row_form(f)
+        if self.editing:
+            # TODO: probably should take `allow_cases` into account here...
+            f.focus_spec = '[name="units_ordered"]'
+
     def download_excel(self):
         """
         Download ordering batch as Excel spreadsheet.