move g_rc_function[] to RC_Channel library

libraries should not rely on data declared in the main program. This
caused a build error for the Desktop build for ArduCopter under cygwin

ArduPlane/ArduPlane.pde

@@ -402,7 +402,6 @@ static unsigned long 	nav_loopTimer;				// used to track the elapsed time for GP
 static unsigned long 	dTnav;						// Delta Time in milliseconds for navigation computations
 static float 			load;						// % MCU cycles used
 
-RC_Channel_aux* g_rc_function[RC_Channel_aux::k_nr_aux_servo_functions];	// the aux. servo ch. assigned to each function
 AP_Relay relay;
 
 ////////////////////////////////////////////////////////////////////////////////

libraries/RC_Channel/RC_Channel_aux.cpp

@@ -3,7 +3,7 @@
 #include <APM_RC.h>
 #include "RC_Channel_aux.h"
 
-extern RC_Channel_aux* g_rc_function[RC_Channel_aux::k_nr_aux_servo_functions];	// the aux. servo ch. assigned to each function
+RC_Channel_aux* g_rc_function[RC_Channel_aux::k_nr_aux_servo_functions];	// the aux. servo ch. assigned to each function
 
 // map a function to a servo channel and output it
 void

libraries/RC_Channel/RC_Channel_aux.h

@@ -44,5 +44,6 @@ public:
 };
 
 void update_aux_servo_function(RC_Channel_aux* rc_5, RC_Channel_aux* rc_6, RC_Channel_aux* rc_7, RC_Channel_aux* rc_8);
+extern RC_Channel_aux* g_rc_function[RC_Channel_aux::k_nr_aux_servo_functions];	// the aux. servo ch. assigned to each function
 
 #endif /* RC_CHANNEL_AUX_H_ */