Introduced new osg::discardDeletedOpenGLObjects() methods, and usage of it in

GrpahicsContext::close() to handle cases where deletingOpenGLObjects is no possible,
such as when GraphicsWindowEmbedded is used.

include/osg/VertexProgram

@@ -217,6 +217,13 @@ class OSG_EXPORT VertexProgram : public StateAttribute
         */
         static void flushDeletedVertexProgramObjects(unsigned int contextID,double currentTime, double& availableTime);
 
+        /** discard all the cached vertex programs which need to be deleted
+          * in the OpenGL context related to contextID.
+          * Note, unlike flush no OpenGL calls are made, instead the handles are all removed.
+          * this call is useful for when an OpenGL context has been destroyed.
+        */
+        static void discardDeletedVertexProgramObjects(unsigned int contextID);
+
         virtual void apply(State& state) const;
 
         virtual void compileGLObjects(State& state) const { apply(state); }