BUG #6593: REASSIGN OWNED fails on extensions

The following bug has been logged on the website:

Bug reference:      6593
Logged by:          Emiliano Leporati
Email address:      emiliano.leporati@gmail.com
PostgreSQL version: 9.1.2
Operating system:   FreeBSD 9.0
Description:=20=20=20=20=20=20=20=20

Steps to reproduce:

postgres=3D# create database failtest;
CREATE DATABASE
postgres=3D# \c failtest
You are now connected to database "failtest" as user "ubik".
failtest=3D# create extension citext;
CREATE EXTENSION
failtest=3D# create table foo(bar integer);
CREATE TABLE
failtest=3D# reassign owned by ubik to dev;
ERROR:  unexpected classid 3079
failtest=3D# select relname from pg_class where oid =3D 3079;
   relname
--------------
 pg_extension
(1 row)

failtest=3D#