Added State::releaseGLObjects() and ShaderComposer::releaseGLObjects() to avoid problems with cleanup of graphics context

include/osg/ShaderComposer

@@ -35,11 +35,12 @@ class OSG_EXPORT ShaderComposer : public osg::Object
 
         virtual osg::Program* getOrCreateProgram(const ShaderComponents& shaderComponents);
 
-
         typedef std::vector< const osg::Shader* >  Shaders;
         virtual osg::Shader* composeMain(const Shaders& shaders);
         virtual void addShaderToProgram(Program* program, const Shaders& shaders);
 
+        void releaseGLObjects(osg::State* state);
+
     protected:
 
         virtual ~ShaderComposer();

include/osg/State

@@ -218,6 +218,9 @@ class OSG_EXPORT State : public Referenced, public Observer
         /** Copy the modes and attributes which capture the current state.*/
         void captureCurrentState(StateSet& stateset) const;
 
+        /** Release all OpenGL objects associated cached by this osg::State object.*/
+        void releaseGLObjects();
+
         /** reset the state object to an empty stack.*/
         void reset();