[patch] Add schema total size to psql \dn+

Hi all,

When we want to get total size of all relation in a schema we have to
execute one of our favorite DBA query. It  is quite simple but what
about displaying schema size when using \dn+ in psql ?

gilles=# \dn+
                               List of schemas
  Name  |  Owner   |  Access privileges   |  Size   |      Description 
--------+----------+----------------------+---------+------------------------
 public | postgres | postgres=UC/postgres+| 608 kB  | standard public schema
        |          | =UC/postgres         |         |
 test   | gilles   |                      | 57 MB   |
 empty  | gilles   |                      | 0 bytes |
(3 rows)

The attached simple patch adds this feature. Is there any cons adding
this information? The patch tries to be compatible to all PostgreSQL
version. Let me know if I have missed something.

Best regards,

--
Gilles Darold
Consultant PostgreSQL
http://dalibo.com - http://dalibo.org