mf2 handlers: handle DisableSource

https://console.cloud.google.com/errors/11063991975010480653

handlers.py

@@ -151,7 +151,9 @@ def get(self, type, source_short_name, string_id, *ids):
       logging.info('Fetching %s', label)
       try:
         obj = self.get_item(*ids)
-      except Exception, e:
+      except models.DisableSource as e:
+        self.abort(401, "Bridgy's access to your account has expired. Please visit https://brid.gy/ to refresh it!")
+      except Exception as e:
         # pass through all API HTTP errors if we can identify them
         code, body = util.interpret_http_exception(e)
         if not code and util.is_connection_failure(e):

test/test_handlers.py

@@ -175,6 +175,16 @@ def test_connection_failures_503(self):
     resp = self.check_response('/post/fake/%s/000', expected_status=503)
     self.assertEqual('FakeSource error:\nTry again pls', resp.body)
 
+  def test_handle_disable_source(self):
+    self.mox.StubOutWithMock(testutil.FakeSource, 'get_activities')
+    testutil.FakeSource.get_activities(
+      activity_id='000', user_id=self.source.key.string_id()
+      ).AndRaise(models.DisableSource())
+    self.mox.ReplayAll()
+
+    resp = self.check_response('/post/fake/%s/000', expected_status=401)
+    self.assertIn("Bridgy's access to your account has expired", resp.body)
+
   def test_comment(self):
     FakeGrSource.comment = {
       'id': 'tag:fa.ke,2013:a1-b2.c3',  # test alphanumeric id (like G+)