Re: sql_drop Event Triggerg

Pushed, with some further minor changes.  One not-so-minor change I
introduced was that pg_event_trigger_dropped_objects() now only works
within a sql_drop event function.  The reason I decided to do this was
that if we don't have that protection, then it is possible to have a
ddl_command_end trigger calling pg_event_trigger_dropped_objects(); and
if there is an sql_drop trigger, then it'd return the list of dropped
objects, but if there's no sql_drop trigger, it'd raise an error.  That
seemed surprising enough action-at-a-distance that some protection is
warranted.

Thanks for all the review.

-- 
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services