pgsql: Fix statistics breakage from bgwriter/checkpointer process split

Fix statistics breakage from bgwriter/checkpointer process split.

ForwardFsyncRequest() supposed that it could only be called in regular
backends, which used to be true; but since the splitup of bgwriter and
checkpointer, it is also called in the bgwriter. We do not want to count
such calls in pg_stat_bgwriter.buffers_backend statistics, so fix things
so that they aren't.

(It's worth noting here that this implies an alarmingly large increase in
the expected amount of cross-process fsync request traffic, which may well
mean that the process splitup was not such a hot idea.)

Branch
------
REL9_2_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/1e9326d6a3efcb5648a85c1653cc263bc787efa0

Modified Files
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src/backend/postmaster/checkpointer.c | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)