Remove RelationGetBufferWithBuffer(), which is horribly confused about

appropriate pin-count manipulation, and instead use ReleaseAndReadBuffer.
Make use of the fact that the passed-in buffer (if there is one) must
be pinned to avoid grabbing the bufmgr spinlock when we are able to
return this same buffer.  Eliminate unnecessary 'previous tuple' and
'next tuple' fields of HeapScanDesc and IndexScanDesc, thereby removing
a whole lot of bookkeeping from heap_getnext() and related routines.

src/include/access/skey.h

@@ -7,8 +7,7 @@
  * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: skey.h,v 1.15 2001/06/01 02:41:36 tgl Exp $
- *
+ * $Id: skey.h,v 1.16 2001/06/09 18:16:59 tgl Exp $
  *
  * Note:
  *		Needs more accessor/assignment routines.
@@ -20,6 +19,7 @@
 #include "access/attnum.h"
 #include "fmgr.h"
 
+
 typedef struct ScanKeyData
 {
 	bits16		sk_flags;		/* flags */
@@ -38,11 +38,6 @@ typedef ScanKeyData *ScanKey;
 #define SK_COMMUTE		0x8		/* commute function (not fully supported) */
 
 
-#define ScanUnmarked			0x01
-#define ScanUncheckedPrevious	0x02
-#define ScanUncheckedNext		0x04
-
-
 /*
  * prototypes for functions in access/common/scankey.c
  */