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/FragmentProgram

@@ -216,6 +216,12 @@ class OSG_EXPORT FragmentProgram : public StateAttribute
           * in the OpenGL context related to contextID.*/
         static void flushDeletedFragmentProgramObjects(unsigned int contextID,double currentTime, double& availableTime);
 
+        /** discard all the cached fragment 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 discardDeletedFragmentProgramObjects(unsigned int contextID);
+
         virtual void apply(State& state) const;
 
         virtual void compileGLObjects(State& state) const { apply(state); }