New syntax for to-be-closed variables

The new syntax is <local *toclose x = f()>. The mark '*' allows other
attributes to be added later without the need of new keywords; it
also allows better error messages.  The API function was also renamed
('lua_tobeclosed' -> 'lua_toclose').

lapi.c

@@ -1207,7 +1207,7 @@ LUA_API int lua_next (lua_State *L, int idx) {
 }
 
 
-LUA_API void lua_tobeclosed (lua_State *L) {
+LUA_API void lua_toclose (lua_State *L) {
   int nresults = L->ci->nresults;
   luaF_newtbcupval(L, L->top - 1);  /* create new to-be-closed upvalue */
   if (!hastocloseCfunc(nresults))  /* function not marked yet? */