Rover: fixed build

APMrover2/APMrover2.pde

@@ -72,6 +72,7 @@
 #include <AP_AHRS.h>         // ArduPilot Mega DCM Library
 #include <AP_NavEKF.h>
 #include <AP_Mission.h>     // Mission command library
+#include <AP_Rally.h>
 #include <AP_Terrain.h>
 #include <PID.h>            // PID library
 #include <RC_Channel.h>     // RC Channel Library

APMrover2/GCS_Mavlink.pde

@@ -517,6 +517,7 @@ bool GCS_MAVLINK::try_send_message(enum ap_message id)
         break;
 
     case MSG_RETRY_DEFERRED:
+    case MSG_TERRAIN:
         break; // just here to prevent a warning
 	}