Little confusing things about client_min_messages.

Hi,

I noticed that the behavior of client_min_messages do not have
a consistency in document and 'pg_settings', postgresql.conf.

----------------
the behaviro is:
I can set 'INFO', 'FATAL' and 'PANIC' as the valid value.

postgres=# set client_min_messages to info;
SET
postgres=# set client_min_messages to fatal;
SET
postgres=# set client_min_messages to panic;
SET

----------------
document says:

        <literal>DEBUG1</>, <literal>LOG</>, <literal>NOTICE</>,
        <literal>WARNING</>, <literal>ERROR</>, <literal>FATAL</>,
        and <literal>PANIC</>.  Each level

I couldn't understand the reason of disappearing 'INFO' from the document.

----------------
pg_settings says:

{debug5,debug4,debug3,debug2,debug1,log,notice,warning,error}

and

postgresql.conf says:

#client_min_messages = notice           # values in order of decreasing detail:
                                        #   debug5
                                        #   debug4
                                        #   debug3
                                        #   debug2
                                        #   debug1
                                        #   log
                                        #   notice
                                        #   warning
                                        #   error


also I couldn't understand the reason of disappearing
'info', 'fatal' and 'panic' from them.
----------------


My proposal is all valid values should be present for users.
I fixed this, please see the attached patch.

regards,
-----------
Tomonari Katsumata