Added support for OpenGL mode black listing to provide better support

for extension checking and invalidation of OpenGL modes associated with
extensions.

src/osg/PointSprite.cpp

@@ -16,6 +16,7 @@
 #include <osg/PointSprite>
 #include <osg/State>
 #include <osg/buffered_value>
+#include <osg/Notify>
 
 using namespace osg;
 
@@ -30,6 +31,16 @@ int PointSprite::compare(const StateAttribute& sa) const
     return 0; // passed all the above comparison macro's, must be equal.
 }
 
+
+bool PointSprite::checkValididityOfAssociatedModes(osg::State& state) const
+{
+
+    bool modeValid = isPointSpriteSupported(state.getContextID());
+    state.setModeValidity(GL_POINT_SPRITE_ARB, modeValid);
+
+    return modeValid;
+}
+
 void PointSprite::apply(osg::State& state) const
 {
     if(!isPointSpriteSupported(state.getContextID())) return;