Add an EXPLAIN (BUFFERS) option to show buffer-usage statistics.

This patch also removes buffer-usage statistics from the track_counts
output, since this (or the global server statistics) is deemed to be a better
interface to this information.

Itagaki Takahiro, reviewed by Euler Taveira de Oliveira.

src/backend/executor/spi.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/spi.c,v 1.211 2009/11/04 22:26:06 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/spi.c,v 1.212 2009/12/15 04:57:47 rhaas Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1908,7 +1908,7 @@ _SPI_execute_plan(SPIPlanPtr plan, ParamListInfo paramLI,
 										plansource->query_string,
 										snap, crosscheck_snapshot,
 										dest,
-										paramLI, false);
+										paramLI, 0);
 				res = _SPI_pquery(qdesc, fire_triggers,
 								  canSetTag ? tcount : 0);
 				FreeQueryDesc(qdesc);