Stack indices changed to union's

That will allow to change pointers to offsets while reallocating
the stack.

lobject.h

@@ -157,6 +157,12 @@ typedef union StackValue {
 /* index to stack elements */
 typedef StackValue *StkId;
 
+
+typedef union {
+  StkId p;  /* actual pointer */
+} StkIdRel;
+
+
 /* convert a 'StackValue' to a 'TValue' */
 #define s2v(o)	(&(o)->val)
 
@@ -618,7 +624,9 @@ typedef struct Proto {
 typedef struct UpVal {
   CommonHeader;
   lu_byte tbc;  /* true if it represents a to-be-closed variable */
-  TValue *v;  /* points to stack or to its own value */
+  union {
+    TValue *p;  /* points to stack or to its own value */
+  } v;
   union {
     struct {  /* (when open) */
       struct UpVal *next;  /* linked list */