sentinel          465 lib/lua/loadlib.c     if (lua_touserdata(L, -1) == sentinel)  /* check loops */
sentinel          488 lib/lua/loadlib.c   lua_pushlightuserdata(L, sentinel);
sentinel          495 lib/lua/loadlib.c   if (lua_touserdata(L, -1) == sentinel) {   /* module did not set a value? */