Flightplan delegate hook for clearing the FP.

This allows delegates to take action when the flightlan is cleared, and especially, for the default delegate in the route-manager to deactivate itself, and hence the GPS LEG mode - which fixes bug 940 I hope.

src/Instrumentation/gps.cxx

@@ -716,7 +716,7 @@ void GPS::routeManagerSequenced()
   if ((index < 0) || (index >= count)) {
     _currentWaypt=NULL;
     _prevWaypt=NULL;
-    SG_LOG(SG_INSTR, SG_ALERT, "GPS: malformed route, index=" << index);
+    // no active leg on the route
     return;
   }
   

src/Navaids/FlightPlan.cxx

@@ -226,6 +226,9 @@ void FlightPlan::clear()
   }
   _legs.clear();  
   
+  if (_delegate) {
+    _delegate->runCleared();
+  }
   unlockDelegate();
 }
   
@@ -1206,4 +1209,10 @@ void FlightPlan::Delegate::runCurrentWaypointChanged()
   currentWaypointChanged();
 }
 
+void FlightPlan::Delegate::runCleared()
+{
+  if (_inner) _inner->runCleared();
+  cleared();
+}  
+  
 } // of namespace flightgear

src/Navaids/FlightPlan.hxx

@@ -104,7 +104,7 @@ public:
     virtual void departureChanged() { }
     virtual void arrivalChanged() { }
     virtual void waypointsChanged() { }
-    
+    virtual void cleared() { }
     virtual void currentWaypointChanged() { }
   
   protected:
@@ -117,6 +117,7 @@ public:
     void runArrivalChanged();
     void runWaypointsChanged();
     void runCurrentWaypointChanged();
+    void runCleared();
       
     friend class FlightPlan;
     

src/Scripting/NasalPositioned.cxx

@@ -1772,6 +1772,11 @@ public:
   {
     callDelegateMethod("currentWaypointChanged");
   }
+    
+  virtual void cleared()
+  {
+    callDelegateMethod("cleared");
+  }
 private:
   
   void callDelegateMethod(const char* method)