BUG #8685: "alter default privileges" cannot revoke default execute privilege on functions

The following bug has been logged on the website:

Bug reference: 8685
Logged by: Manuel Zahariev
Email address: mz(at)alumni(dot)sfu(dot)ca
PostgreSQL version: 9.1.11
Operating system: Ubuntu 13.10
Description:

ALTER DEFAULT PRIVILEGES REVOKE EXECUTE ON FUNCTIONS FROM <role>
...does not remove default execute privileges on functions

====================
Log:

$sudo -u postgres psql
psql (9.1.11)
Type "help" for help.

postgres=# CREATE DATABASE db;
CREATE DATABASE
postgres=# CREATE ROLE u WITH PASSWORD '1234' login;
CREATE ROLE
postgres=# \c db
You are now connected to database "db" as user "postgres".
db=# ALTER DEFAULT PRIVILEGES REVOKE EXECUTE ON FUNCTIONS FROM u;
ALTER DEFAULT PRIVILEGES
db=# CREATE FUNCTION f() RETURNS varchar AS $$
db$# SELECT 'Hello'::varchar;
db$# $$ LANGUAGE 'SQL' SECURITY DEFINER;
CREATE FUNCTION
db=# SELECT * FROM f();
f
-------
Hello
(1 row)

db=# \q
$psql -h localhost db u
Password for user u:
psql (9.1.11)
SSL connection (cipher: DHE-RSA-AES256-SHA, bits: 256)
Type "help" for help.

db=> SELECT * FROM f(); -- should fail
f
-------
Hello
(1 row)