it now maintains references to the last applied matrices, automatically doing
lazy state updating. This simplifies the various places in the OSG which
were previously doing the applying, add paves the way for managing the
projection matrix within the scene graph.
Remove MemoryAdapter and mem_ptr as they arn't being used, and can potentially
confuse users by their existance.
Moved CullVisitor/RenderStage/RenderStageLighting across to managing lights
entirely within RenderStageLighting, and changed the management of modelview
matrices so that RenderLeaf now stores the absolute modelview matrix, rather
than a model matrix as done previously. The later allows RenderLeaf's to do
a glLoadMatrix rather than a glPushMatrix/glMultMatrix/glPopMatrix.
