pgsql: Flush any remaining statistics counts out to the collector at

Log Message:
-----------
Flush any remaining statistics counts out to the collector at process
exit.  Without this, operations triggered during backend exit (such as
temp table deletions) won't be counted ... which given heavy usage of
temp tables can lead to pg_autovacuum falling way behind on the need
to vacuum pg_class and pg_attribute.  Per reports from Steve Crawford
and others.

Tags:
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REL7_4_STABLE

Modified Files:
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    pgsql/src/backend/postmaster:
        pgstat.c (r1.45.2.2 -> r1.45.2.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/pgstat.c.diff?r1=1.45.2.2&r2=1.45.2.3)