luaL_checkudata (5.1-rc4) bug ?

[Jérôme VOLPOËT <jerome.volpoet@...>]

Hello everyone,

I'm using 5.02 for a while and tried to install 5.1rc4.

It seems that there is a bug in the new implementation of luaL_checkudata :
Everything works fine if the index ( ud ) is positive, but there seems to be 
a problem when it's negative :

for example, I use it with index -1, the result is that it throw an error : 
the lua_getmetatable used in the test try to extract metatable from the 
result of lua_getfield( at index -1 ) but not of my own usertype (which is 
now a index -2)

Am I right, or am I doing somthing wrong elsewhere ?