Copter: fixed build error

thanks to Marco for pointing this out

ArduCopter/ArduCopter.pde

@@ -58,6 +58,7 @@
 #include <avr/io.h>
 #include <avr/eeprom.h>
 #include <avr/pgmspace.h>
+#include <avr/wdt.h>
 #include <math.h>
 
 // Libraries

ArduCopter/GCS_Mavlink.pde

@@ -1060,7 +1060,7 @@ void GCS_MAVLINK::handleMessage(mavlink_message_t* msg)
         mavlink_msg_command_long_decode(msg, &packet);
         if (mavlink_check_target(packet.target_system, packet.target_component)) break;
 
-        uint8_t result;
+        uint8_t result = MAV_RESULT_UNSUPPORTED;
 
         // do command
         send_text(SEVERITY_LOW,PSTR("command received: "));