ME TIRA DESTA LISTA, POR FAVOR!!!
> > I've noticed that luaL_checkudata cannot be used with a negative stack
> > index; that is, one relative to the top of the stack. The difficulty
> > is that it fetches the metatable from the registry before it fetches
> > the metatable from the userdata to be checked, so the stack depth
> > has changed by the time it does that.
>
> I think this is fixed in 5.1.1.
>
