Added support into osgProducer::Viewer for flushing and compiling GL objects

via a Producer post swap callback.

include/osgUtil/SceneView

@@ -430,6 +430,9 @@ class OSGUTIL_EXPORT SceneView : public osg::Referenced
         /** Do draw traversal of draw bins generated by cull traversal.*/
         virtual void draw();
         
+        /** Flush all the OpenGL objects, such as texture objects, display lists etc.*/
+        virtual void flushDeletedGLObjects(double& availableTime);
+        
     protected:
 
         virtual ~SceneView();
@@ -493,6 +496,8 @@ class OSGUTIL_EXPORT SceneView : public osg::Referenced
         
         GLenum                                      _drawBufferValue;
         
+        bool                                        _requiresFlush;
+        
 };
 
 }