1) this makes help() work nicely on vtk classes, since __dict__ is used for introspection
     2) since __dict__ is a hash, VTK function calls no longer require a linear lookup and should be faster than before
     The __dict__ is only created for VTK classes that are actually used, so the memory overhead should be small.  Note that VTK classes and instances no longer have __members__ or __methods__ special attributes.