Added reset of the State::CurrentVertexArrayState() to prevent the State::_vas becoming a dangling pointer when VertexArrayState objects are deleted.

include/osg/State

@@ -549,6 +549,9 @@ class OSG_EXPORT State : public Referenced
         /** Set the getCurrentVertexArrayState to the GlobalVertexArrayState.*/
         void setCurrentToGlobalVertexArrayState() { _vas = _globalVertexArrayState.get(); }
 
+        /** Reset the CurrentVertexArrayObject if it's value equals the specificied vas - use when deleting a vas.*/
+        void resetCurrentVertexArrayStateOnMatch(VertexArrayState* vas) { if (_vas==vas) _vas = 0; }
+
 
         /** disable the vertex, normal, color, tex coords, secondary color, fog coord and index arrays.*/
         void disableAllVertexArrays();