Fix error when downloading large file

The Livescribe SmartPen firmware (at least v1.5) requires a Connection header after every Continue response (which contradicts the Obex spec). We convince openobex to send the header by calling OBEX_ObjectAddHeader in the event callback.

The problem is that openobex keeps counting request bytes, and when you set OBEX_FL_FIT_ONE_PACKET it will return error once all your Connection headers reach the 1kB MTU. The solution is to turn off that flag.