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_0_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/cd5316f67d5f6e110205d47d27b11eb644720e4b

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