Mps: feedback branch: merge source-only corrections from master:

PARENT macro comment; TractArena macro.  No run-time effect.

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 Change: 160624
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mps/code/misc.h

@@ -137,13 +137,14 @@ typedef const struct SrcIdStruct {
 /* PARENT -- parent structure
  *
  * Given a pointer to a field of a structure this returns a pointer to
- * the main structure.  PARENT(foo_t, x, foo->x) == foo.
+ * the main structure.  PARENT(foo_t, x, &(foo->x)) == foo.
  *
  * This macro is thread-safe, see design.mps.misc.parent.thread-safe.
  *
  * That intermediate (void *) is required to stop some compilers complaining
  * about alignment of 'type *' being greater than that of 'char *'.  Which
- * is true, but not a bug, since p really is a pointer into a 'type' struct.
+ * is true, but not a bug, since the result really is a pointer to a 'type'
+ * struct.
  */
 
 #define PARENT(type, field, p) \

mps/code/tract.c

@@ -22,7 +22,7 @@ static void ChunkDecache(Arena arena, Chunk chunk);
 
 /* TractArena -- get the arena of a tract */
 
-#define TractArena(seg) PoolArena(TractPool(tract))
+#define TractArena(tract) PoolArena(TractPool(tract))
 
 
 /* TractCheck -- check the integrity of a tract */