2 bugs and 1 change

- 2 bugs:
1. Error field in the JSON result from the facebook server should not be
   processed in FbBatch. They should be handled by the callers of FbBatch.
2. FbBatch throws Exception, not FacebookApiException

- 1 change
1. Add "Sorry, you are blocked from leaving comments due to continued
   overuse of this feature." in the facebook error handling routine.