lua_rawequal
if (!lua_rawequal(L, -1, -2)) /* not the same? */
if (lua_rawequal(L, objidx, -1)) { /* found object? */
lua_pushboolean(L, lua_rawequal(L, 1, 2));
LUA_API int (lua_rawequal) (lua_State *L, int idx1, int idx2);