#738: crash when switching 2D panels

FGPanelNode doesn't always own its "_panel" object - so it's not ok to
always delete it. Use ref-counting/smart-pointers instead.

src/Main/fg_commands.cxx

@@ -414,7 +414,6 @@ do_panel_load (const SGPropertyNode * arg)
   }
   SG_LOG(SG_INPUT, SG_INFO, "Loaded new panel from " << panel_path);
   globals->get_current_panel()->unbind();
-  delete globals->get_current_panel();
   globals->set_current_panel( new_panel );
   globals->get_current_panel()->bind();
   return true;

src/Main/globals.cxx

@@ -188,7 +188,7 @@ FGGlobals::~FGGlobals()
     delete mag;
     delete matlib;
     delete route_mgr;
-    delete current_panel;
+    current_panel = NULL;
 
     delete ATC_mgr;
 

src/Main/globals.hxx

@@ -119,7 +119,7 @@ private:
     FGRouteMgr *route_mgr;
 
     // 2D panel
-    FGPanel *current_panel;
+    SGSharedPtr<FGPanel> current_panel;
 
     // ATC manager
     FGATCMgr *ATC_mgr;

src/Model/panelnode.cxx

@@ -153,7 +153,6 @@ void FGPanelNode::initWithPanel()
 
 FGPanelNode::~FGPanelNode()
 {
-    delete _panel;
 }
 
 osg::Matrix FGPanelNode::transformMatrix() const

src/Model/panelnode.hxx

@@ -4,6 +4,7 @@
 #include <osg/Vec3>
 #include <osg/Matrix>
 #include <osg/Drawable>
+#include <simgear/structure/SGSharedPtr.hxx>
 
 class FGPanel;
 class SGPropertyNode;
@@ -43,7 +44,7 @@ public:
 private:
     void initWithPanel();
     
-    FGPanel* _panel;
+    SGSharedPtr<FGPanel> _panel;
   
     bool _resizeToViewport;