__type for better typing

[Timm Felden <timm.felden@...>]

Is there any *good* way to get the type of a table or userdata. I'm 
thinking of types like "Vector" or "Sprite" or something else, that I am 
using internally. Currently I'm using typechecking with the 
REGISTRYINDEX but I it doesn't work with my new OOP System.
So I came up with the idea to add an __type field to the metatable but 
this would mean to me, that I have to implement a new gettype function. 
Maybe someone has a better idea:)