GIN's ItemPointerIsMin, ItemPointerIsMax, and ItemPointerIsLossyPage macros

should use GinItemPointerGetBlockNumber/GinItemPointerGetOffsetNumber,
not ItemPointerGetBlockNumber/ItemPointerGetOffsetNumber, because the latter
will Assert() on ip_posid == 0, ie a "Min" pointer.  (Thus, ItemPointerIsMin
has never worked at all, but it seems unused at present.)  I'm not certain
that the case can occur in normal functioning, but it's blowing up on me
while investigating Tatsuo-san's data corruption problem.  In any case it
seems like a problem waiting to bite someone.

Back-patch just in case this really is a problem for somebody in the field.

src/include/access/gin.h

@@ -4,7 +4,7 @@
  *
  *	Copyright (c) 2006-2009, PostgreSQL Global Development Group
  *
- *	$PostgreSQL: pgsql/src/include/access/gin.h,v 1.31 2009/03/25 22:19:01 tgl Exp $
+ *	$PostgreSQL: pgsql/src/include/access/gin.h,v 1.32 2009/06/05 18:50:47 tgl Exp $
  *--------------------------------------------------------------------------
  */
 #ifndef GIN_H
@@ -124,18 +124,18 @@ typedef struct GinMetaPageData
 #define ItemPointerSetMin(p)  \
 	ItemPointerSet((p), (BlockNumber)0, (OffsetNumber)0)
 #define ItemPointerIsMin(p)  \
-	(ItemPointerGetOffsetNumber(p) == (OffsetNumber)0 && \
-	 ItemPointerGetBlockNumber(p) == (BlockNumber)0)
+	(GinItemPointerGetOffsetNumber(p) == (OffsetNumber)0 && \
+	 GinItemPointerGetBlockNumber(p) == (BlockNumber)0)
 #define ItemPointerSetMax(p)  \
 	ItemPointerSet((p), InvalidBlockNumber, (OffsetNumber)0xffff)
 #define ItemPointerIsMax(p)  \
-	(ItemPointerGetOffsetNumber(p) == (OffsetNumber)0xffff && \
-	 ItemPointerGetBlockNumber(p) == InvalidBlockNumber)
+	(GinItemPointerGetOffsetNumber(p) == (OffsetNumber)0xffff && \
+	 GinItemPointerGetBlockNumber(p) == InvalidBlockNumber)
 #define ItemPointerSetLossyPage(p, b)  \
 	ItemPointerSet((p), (b), (OffsetNumber)0xffff)
 #define ItemPointerIsLossyPage(p)  \
-	(ItemPointerGetOffsetNumber(p) == (OffsetNumber)0xffff && \
-	 ItemPointerGetBlockNumber(p) != InvalidBlockNumber)
+	(GinItemPointerGetOffsetNumber(p) == (OffsetNumber)0xffff && \
+	 GinItemPointerGetBlockNumber(p) != InvalidBlockNumber)
 
 typedef struct
 {