pgsql: Add a bit of debug logging to backend_read_statsfile().

Add a bit of debug logging to backend_read_statsfile().

This is in hopes of learning more about what causes "pgstat wait timeout"
warnings in the buildfarm.  This patch should probably be reverted once
we've learned what we can.  As coded, it will result in regression test
"failures" at half the delay that the existing code does, so I expect
to see a few more than before.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/79b2ee20c8a041a85dd230c4e787bef22edae57b

Modified Files
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src/backend/postmaster/pgstat.c |   29 +++++++++++++++++++++++++----
1 files changed, 25 insertions(+), 4 deletions(-)