Still more paranoia in PageAddItem: disallow specification of an item

offset past the last-used-item-plus-one, since that would result in
leaving uninitialized holes in the item pointer array.  AFAICT the only
place that was depending on this was btree index build, which was being
cavalier about when to fill in the P_HIKEY pointer; easily fixed.
Also a small performance improvement: shuffle itemid's by means of
memmove, not a one-at-a-time loop.

src/backend/access/nbtree/nbtsort.c

@@ -35,7 +35,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtsort.c,v 1.65 2002/07/02 05:48:44 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtsort.c,v 1.66 2002/08/06 19:41:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -187,10 +187,17 @@ _bt_blnewpage(Relation index, Buffer *buf, Page *page, int flags)
 
 	*buf = _bt_getbuf(index, P_NEW, BT_WRITE);
 	*page = BufferGetPage(*buf);
+
+	/* Zero the page and set up standard page header info */
 	_bt_pageinit(*page, BufferGetPageSize(*buf));
+
+	/* Initialize BT opaque state */
 	opaque = (BTPageOpaque) PageGetSpecialPointer(*page);
 	opaque->btpo_prev = opaque->btpo_next = P_NONE;
 	opaque->btpo_flags = flags;
+
+	/* Make the P_HIKEY line pointer appear allocated */
+	((PageHeader) *page)->pd_lower += sizeof(ItemIdData);
 }
 
 /*