Add fancy locking to oauth2client.

Reviewed in http://codereview.appspot.com/4919049/
diff --git a/tests/test_oauth2client_appengine.py b/tests/test_oauth2client_appengine.py
index fd06668..f9b5094 100644
--- a/tests/test_oauth2client_appengine.py
+++ b/tests/test_oauth2client_appengine.py
@@ -191,8 +191,8 @@
                      self.decorator.credentials.access_token)
 
     # Invalidate the stored Credentials
-    self.decorator.credentials._invalid = True
-    self.decorator.credentials.store(self.decorator.credentials)
+    self.decorator.credentials.invalid = True
+    self.decorator.credentials.store.put(self.decorator.credentials)
 
     # Invalid Credentials should start the OAuth dance again
     response = self.app.get('/foo_path')