Copter: call mission.init during startup

ArduCopter/system.pde

@@ -287,6 +287,9 @@ static void init_ardupilot()
     init_sonar();
 #endif
 
+    // initialise mission library
+    mission.init();
+
     // initialise the flight mode and aux switch
     // ---------------------------
     reset_control_switch();