pgsql: Log a better message when canceling autovacuum.

Log a better message when canceling autovacuum.

The old message was at DEBUG2, so typically it didn't show up in the
log at all. As a result, in most cases where autovacuum was canceled,
the only information that was logged was the table being vacuumed,
with no indication as to what problem caused the cancel. Crank up
the level to LOG and add some more details to assist with debugging.

Back-patch all the way, per discussion on pgsql-hackers.

Branch
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REL9_2_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/a5bca2487244e48de1ece92d4c6a1ff330d5333c

Modified Files
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src/backend/storage/lmgr/proc.c | 25 +++++++++++++++++++++----
1 files changed, 21 insertions(+), 4 deletions(-)