new list 'twups' to allow traversal of upvalues from dead threads

(+ fixed some problems with cycles involving those upvalues)

lfunc.h

@@ -1,5 +1,5 @@
 /*
-** $Id: lfunc.h,v 2.11 2013/09/11 15:17:00 roberto Exp roberto $
+** $Id: lfunc.h,v 2.12 2014/02/15 13:12:01 roberto Exp roberto $
 ** Auxiliary functions to manipulate prototypes and closures
 ** See Copyright Notice in lua.h
 */
@@ -18,6 +18,10 @@
                          cast(int, sizeof(TValue *)*((n)-1)))
 
 
+/* test whether thread is in 'twups' list */
+#define isintwups(L)	(L->twups != L)
+
+
 /*
 ** Upvalues for Lua closures
 */