Add buffer access counters to pg_stat_statements.

Itagaki Takahiro <itagaki.takahiro@gmail.com>

Commit: 8964dbd51e4e3e7ea179f85b46ce52715383d869
Author: Itagaki Takahiro <itagaki.takahiro@gmail.com>
Date: 2010-01-08T00:38:20Z
Releases: 9.0.0
Add buffer access counters to pg_stat_statements.

This uses the same infrastructure with EXPLAIN BUFFERS to support
{shared|local}_blks_{hit|read|written} andtemp_blks_{read|written}
columns in the pg_stat_statements view. The dumped file format
also updated.

Thanks to Robert Haas for the review.

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