BUG #11884: pg_dump / restore mangles IS DISTINCT FROM expressions

The following bug has been logged on the website:

Bug reference: 11884
Logged by: Nick Barnes
Email address: nickbarnes01(at)gmail(dot)com
PostgreSQL version: 9.3.5
Operating system: CentOS 6.5
Description:

IS DISTINCT FROM expressions are not dumped/restored correctly if the
comparison operator is outside the search path. e.g.:

psql <<EOF
CREATE DATABASE test1;
CREATE DATABASE test2;
\c test1;
CREATE SCHEMA s;
CREATE EXTENSION citext SCHEMA s;
SET search_path TO public, s;
CREATE TABLE t (x citext CHECK (x IS DISTINCT FROM ''));
EOF
pg_dump -d test1 | psql -d test2
psql -d test2 -c '\d t'

The check constraint is restored as (x::text IS DISTINCT FROM
''::s.citext::text), i.e. using the <>(text,text) operator instead of
<>(citext,citext).