Remove global variable scanCommandId in favor of storing a command ID

in snapshots, per my proposal of a few days ago.  Also, tweak heapam.c
routines (heap_insert, heap_update, heap_delete, heap_mark4update) to
be passed the command ID to use, instead of doing GetCurrentCommandID.
For catalog updates they'll still get passed current command ID, but
for updates generated from the main executor they'll get passed the
command ID saved in the snapshot the query is using.  This should fix
some corner cases associated with functions and triggers that advance
current command ID while an outer query is still in progress.

src/backend/commands/portalcmds.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/portalcmds.c,v 1.1 2002/04/15 05:22:03 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/portalcmds.c,v 1.2 2002/05/21 22:05:54 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -74,7 +74,6 @@ PerformPortalFetch(char *name,
 	EState	   *estate;
 	MemoryContext oldcontext;
 	ScanDirection direction;
-	CommandId	savedId;
 	bool		temp_desc = false;
 
 	/* initialize completion status in case of early exit */
@@ -131,14 +130,6 @@ PerformPortalFetch(char *name,
 		temp_desc = true;
 	}
 
-	/*
-	 * Restore the scanCommandId that was current when the cursor was
-	 * opened.  This ensures that we see the same tuples throughout the
-	 * execution of the cursor.
-	 */
-	savedId = GetScanCommandId();
-	SetScanCommandId(PortalGetCommandId(portal));
-
 	/*
 	 * Determine which direction to go in, and check to see if we're
 	 * already at the end of the available tuples in that direction.  If
@@ -185,11 +176,6 @@ PerformPortalFetch(char *name,
 				 (dest == None) ? "MOVE" : "FETCH",
 				 estate->es_processed);
 
-	/*
-	 * Restore outer command ID.
-	 */
-	SetScanCommandId(savedId);
-
 	/*
 	 * Clean up and switch back to old context.
 	 */