lo_manage trigger on updates

Hi all,

I think the doc section about using lo_manage() as a trigger:
   http://www.postgresql.org/docs/current/static/lo.html

could have its example tweaked to use a column-level BEFORE UPDATE
trigger, so as to save unnecessary trigger firings. Something like the
attached, perhaps?

On a similar note, the warning on that page about truncates could be
softened if we extended the lo_manage() function to handle truncates,
and set it up as on ON TRUNCATE trigger as well.

Josh