AC_WPNav: disabled broken example build

this test doesn't actually do anything yet

libraries/AC_WPNav/examples/AC_WPNav_test/AC_WPNav_test.pde

@@ -12,6 +12,7 @@
 
 #include <AP_GPS.h>             // ArduPilot GPS library
 #include <AP_ADC.h>             // ArduPilot Mega Analog to Digital Converter Library
+#include <AP_ADC_AnalogSource.h>
 #include <AP_Baro.h>            // ArduPilot Mega Barometer Library
 #include <Filter.h>
 #include <AP_Compass.h>         // ArduPilot Mega Magnetometer Library