[HACKERS] IF [NOT] EXISTS for replication slots

Hi all,

Lately I have bumped into a case where it would have been useful to
make the difference between a failure because of a slot already
dropped and an internal failure of Postgres. Is there any interest for
support of IE and INE for CREATE and DROP_REPLICATION_SLOT?
My use case involved only the SQL-callable interface, but I would
think that it is useful to make this difference as well with the
replication protocol. For the function we could just add a boolean
argument to control the switch, and for the replication commands a
dedicated keyword.

Any thoughts?
-- 
Michael