i have not yet ordered a gps :)
and the code does not compile - and prob. never has been tested.
the variable/class AP_GPS_NONE does not exist.
it is sligthly different - in the ArduPilotMega you have to refelct the correct speeling.
locate for the line in bold and change it as written below:
#elif GPS_PROTOCOL == GPS_PROTOCOL_NONE
# error Must define GPS_PROTOCOL in your configuration file.
change it in your project and then it compiles.