Repair longstanding error in btree xlog replay: XLogReadBuffer should be

passed extend = true whenever we are reading a page we intend to reinitialize
completely, even if we think the page "should exist".  This is because it
might indeed not exist, if the relation got truncated sometime after the
current xlog record was made and before the crash we're trying to recover
from.  These two thinkos appear to explain both of the old bug reports
discussed here:
http://archives.postgresql.org/pgsql-hackers/2005-05/msg01369.php

src/backend/access/nbtree/nbtxlog.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtxlog.c,v 1.27 2006/03/24 04:32:12 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtxlog.c,v 1.28 2006/03/28 21:17:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -243,7 +243,7 @@ btree_xlog_split(bool onleft, bool isroot,
 	rightsib = (onleft) ? xlrec->otherblk : targetblk;
 
 	/* Left (original) sibling */
-	buffer = XLogReadBuffer(false, reln, leftsib);
+	buffer = XLogReadBuffer(true, reln, leftsib);
 	if (!BufferIsValid(buffer))
 		elog(PANIC, "btree_split_redo: lost left sibling");
 
@@ -504,7 +504,7 @@ btree_xlog_delete_page(bool ismeta,
 	}
 
 	/* Rewrite target page as empty deleted page */
-	buffer = XLogReadBuffer(false, reln, target);
+	buffer = XLogReadBuffer(true, reln, target);
 	if (!BufferIsValid(buffer))
 		elog(PANIC, "btree_delete_page_redo: lost target page");
 	page = (Page) BufferGetPage(buffer);