pgsql: Defend against bad trigger definitions in contrib/lo's lo_manage

Defend against bad trigger definitions in contrib/lo's lo_manage() trigger.

This function formerly crashed if called as a statement-level trigger,
or if a column-name argument wasn't given.

In passing, add the trigger name to all error messages from the function.
(None of them are expected cases, so this shouldn't pose any compatibility
risk.)

Marc Cousin, reviewed by Sawada Masahiko

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/af1288e6812367dfb11f5b3cadb432fed74e2cd7

Modified Files
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contrib/lo/lo.c |   14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)