pgsql: Add some temporary instrumentation to pgstat.c.

Add some temporary instrumentation to pgstat.c.

Log main-loop blocking events and the results of inquiry messages.
This is to get some clarity as to what's happening on those Windows
buildfarm members that still don't like the latch-ified stats collector.
This bulks up the postmaster log a tad, so I won't leave it in place for
long.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/7d88bb73f755f7fb5d847ef2319c21076054fb0e

Modified Files
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src/backend/postmaster/pgstat.c | 20 ++++++++++++++++++++
1 files changed, 20 insertions(+), 0 deletions(-)