To-be-closed variables in the C API

ltests.c

@@ -1554,6 +1554,9 @@ static struct X { int x; } x;
       int i = getindex;
       return lua_yieldk(L1, nres, i, Cfunck);
     }
+    else if EQ("tobeclosed") {
+      lua_tobeclosed(L);
+    }
     else luaL_error(L, "unknown instruction %s", buff);
   }
   return 0;