First "complete" implementation of to-be-closed variables

Still missing:
- handling of memory errors when creating upvalue (must run closing
method all the same)
- interaction with coroutines

lstate.c

@@ -258,7 +258,7 @@ static void preinit_thread (lua_State *L, global_State *g) {
 
 static void close_state (lua_State *L) {
   global_State *g = G(L);
-  luaF_close(L, L->stack);  /* close all upvalues for this thread */
+  luaF_close(L, L->stack, -1);  /* close all upvalues for this thread */
   luaC_freeallobjects(L);  /* collect all objects */
   if (ttisnil(&g->nilvalue))  /* closing a fully built state? */
     luai_userstateclose(L);
@@ -301,7 +301,7 @@ LUA_API lua_State *lua_newthread (lua_State *L) {
 
 void luaE_freethread (lua_State *L, lua_State *L1) {
   LX *l = fromstate(L1);
-  luaF_close(L1, L1->stack);  /* close all upvalues for this thread */
+  luaF_close(L1, L1->stack, -1);  /* close all upvalues for this thread */
   lua_assert(L1->openupval == NULL);
   luai_userstatefree(L, L1);
   freestack(L1);