Unmark as invalid when token can be refreshed

It is totally possible that the server (in a bad state) responds temporarily with an "invalid x" and on a retry actually refreshes the token. So we need to reset the flag ´self.invalid´.

Author: kaste

oauth2client/client.py

@@ -742,6 +742,9 @@ def _do_refresh_request(self, http_request):
             seconds=int(d['expires_in'])) + datetime.datetime.utcnow()
       else:
         self.token_expiry = None
+      # On temporary refresh errors, the user does not actually have to
+      # re-authorize, so we unflag here.
+      self.invalid = False
       if self.store:
         self.store.locked_put(self)
     else: