metatable for the registry?

[Josh Haberman <jhaberman@...>]

Is setting a metatable on the registry supported?  Should it be?

I ask because I was reading the source to luaL_checkudata() and noticed
that it uses lua_getfield() to read from the registry instead of
lua_rawget().  I was wondering if it would be more efficient to do a 
rawget instead.

Setting a metatable on the registry seems like a bad idea since it by 
definition a shared resource.

Josh