mavproxy_fence.py: create apply_function_to_point

... and a convenience push_to_vehicle method

MAVProxy/modules/mavproxy_fence.py

@@ -256,6 +256,15 @@ def add_polyfence(self, fence_type, points):
             items.append(m)
 
         self.append(items)
+        self.push_to_vehicle()
+
+    def apply_function_to_points(self, function):
+        if not self.check_have_list():
+            return
+        for i in range(self.wploader.count()):
+            function(i, self.wploader.item(i))
+
+    def push_to_vehicle(self):
         self.send_all_items()
         self.wploader.last_change = time.time()