patch (for 9.1) string functions

Hello

this patch contains a string formatting function "format"

postgres=# select format('some message: % (current user: %)',
current_date, current_user);
                     format
------------------------------------------------
 some message: 2010-03-09 (current user: pavel)
(1 row)

this patch add new contrib module string functions - contains mainly
sprintf function:

postgres=# select sprintf('some message: %10s (%10s)', current_date,
current_user);
                sprintf
---------------------------------------
 some message: 2010-03-09 (     pavel)
(1 row)

postgres=# select sprintf('some message: %10s (%-10s)', current_date,
current_user);
                sprintf
---------------------------------------
 some message: 2010-03-09 (pavel     )
(1 row)


some string variadic functions

postgres=# select concat('ahaha',10,null,current_date, true);
         concat
------------------------
 ahaha,10,,2010-03-09,t
(1 row)

postgres=# select concat_sql('ahaha',10,null,current_date, true);
           concat_sql
--------------------------------
 'ahaha',10,NULL,'2010-03-09',t
(1 row)

postgres=# select concat_json('ahaha'::text,10,null,current_date, true);
            concat_json
-----------------------------------
 "ahaha",10,null,"2010-03-09",true
(1 row)


and some basic text function rvrs, left, right.

Regards
Pavel Stehule