Reset: ensure FGODGuage shutsdown cleanly.

- remove ODGuage instances during shutdown phase (don't wait until
deletion)

src/Cockpit/wxradar.cxx

@@ -118,7 +118,6 @@ wxRadarBg::wxRadarBg(SGPropertyNode *node) :
 wxRadarBg::~wxRadarBg ()
 {
     _font_node->removeChangeListener(this);
-    delete _odg;
 }
 
 
@@ -249,6 +248,11 @@ wxRadarBg::init ()
     _time = 0.0;
 }
 
+void wxRadarBg::shutdown()
+{
+    delete _odg;
+    _odg = NULL;
+}
 
 // Local coordinates for each echo
 const osg::Vec3f echoCoords[4] = {

src/Cockpit/wxradar.hxx

@@ -44,6 +44,8 @@ public:
     virtual ~wxRadarBg();
 
     virtual void init();
+    virtual void shutdown();
+    
     virtual void update(double dt);
     virtual void valueChanged(SGPropertyNode *);