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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REL8_4_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/2c3b7d2247d8989c4ef726ecdd65817c02afbf69

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