This makes Nominatim compatible with osm2pgsql's default update
modus operandi of deleting and reinserting data. Deletes are diverted
into a TODO table instead of executing them. When data is reinserted,
the corresponding entry in the TODO table is deleted. After updates are
finished, the remaining entries in the TODO table are executed, doing
the same work as the delete trigger did before.
The new behaviour also works against the gazetteer output with its
insert-only mechanism.
The gazetteer output doesn't disable these functions when
writing to the place table but the triggers may contain
operations that cause misplanning for the query planner.
This is a exception to be thrown when the error occures because
of bad user data. We don't want to print a full stack trace in
these cases but just tell the user what went wrong.
