Change the source code for building under Mac OS X.

Change the source code for building under Mac OS X 10.8.

Build without Error or Warnings.
Funktion used and see a reaction at the TX connector from the bladeRF with this tool https://github.com/maggo1404/bladeRF_examples/tree/libusb_support/simple_examples/blade_send_tone :
- Open device
- Set Frequenz
- Set tx Gain
- Send a sinus 
- Enable/Disable TX
- Close device
- Set samplerate
- Set filter bandwith