issues fixed

Hello Shaioz, 

On behalf of our communication within the forum on May 21st, I've fixed the following issues:
- do not retry on intentional errors #4
- [Feature Request] Add a setting / flag to suppress NSLog #3

The library is carefully tested within our medical project (doing magic with http requests) and it works perfectly.

I would like to ask if you may pull my request, to participate and improve your awesome AFNetworking extension.