Restructred the enabling of vertex array object support to allow one to set enable the default via osg::State.

Added OSG_VERTEX_BUFFER_HINT env var to osg::DisplaySettings with VERTEX_BUFFER_OBJECT/VBO, VERTEX_ARRAY_OBJECT/VAO and NO_PREFERENCE to allow one to foce on VBO or VAO usage.

Restructred BufferObject assigned in osg::Geometry

Added

src/osg/VertexArrayState.cpp

@@ -719,3 +719,9 @@ void VertexArrayState::setInterleavedArrays( osg::State& state, GLenum format, G
     dirtyAllVertexArrays();
 #endif
 }
+
+void VertexArrayState::dirty()
+{
+    setRequiresSetArrays(true);
+}
+