If you built your AirPi as suggested on http://airpi.es , no customization on outputs/lcd.py is needed.
The only thing you have to do, is adding the lcd output to your outputs.cfg:
The code supports the Adafruit LCD-PiPlate with all different LCD displays (monochrome positive or negative and rgb):
If You own a raspberry pi of the first generation (256MB RAM), You probably have to change the bus numbering. Look at https://learn.adafruit.com/adafruit-16x2-character-lcd-plus-keypad-for-raspberry-pi/usage