pgsql: New GUC, track_iotiming, to track I/O timings.

New GUC, track_iotiming, to track I/O timings.

Currently, the only way to see the numbers this gathers is via
EXPLAIN (ANALYZE, BUFFERS), but the plan is to add visibility through
the stats collector and pg_stat_statements in subsequent patches.

Ants Aasma, reviewed by Greg Smith, with some further changes by me.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/40b9b957694cf7749c420c6c51a7e1d3c9b1fec1

Modified Files
--------------
doc/src/sgml/config.sgml | 15 +++++++++++++++
src/backend/commands/explain.c | 18 ++++++++++++++++++
src/backend/executor/instrument.c | 2 ++
src/backend/storage/buffer/bufmgr.c | 24 ++++++++++++++++++++++++
src/backend/utils/misc/guc.c | 9 +++++++++
src/backend/utils/misc/postgresql.conf.sample | 1 +
src/include/executor/instrument.h | 2 ++
src/include/storage/bufmgr.h | 1 +
8 files changed, 72 insertions(+), 0 deletions(-)