Re: doc - add missing documentation for "acldefault"

>> postgres=# \df acl*
>> List of fun
>>    Schema   |    Name     | Result data type |
>> ------------+-------------+------------------+----------------------------------
>>  pg_catalog | aclcontains | boolean          | aclitem[], aclitem
>>  pg_catalog | acldefault  | aclitem[]        | "char", oid
>>  pg_catalog | aclexplode  | SETOF record     | acl aclitem[], OUT grantor
>> oid, O
>>  pg_catalog | aclinsert   | aclitem[]        | aclitem[], aclitem
>>  pg_catalog | aclitemeq   | boolean          | aclitem, aclitem
>>  pg_catalog | aclitemin   | aclitem          | cstring
>>  pg_catalog | aclitemout  | cstring          | aclitem
>>  pg_catalog | aclremove   | aclitem[]        | aclitem[], aclitem
>
> Some of them are definitely internal. For example, aclitemin and
> aclitemout are input and output functions respectively of the aclitem
> data type. I think they don't need to be documented and shouldn't have
> "pg_" prefix as they was created to maintenance aclitem data type.

Indeed, some are internal for managing the type itself. Maybe that 
encompasses also "aclitemeq", not sure. I would see no harm in having them 
documented though.

ISTM that acl{contains,default,explode,insert,remove} deserve a real doc.

-- 
Fabien.