String concatenation work in version 8.2.11 and 8.3.6

hi,all
for example tableA
create table tableA (
id serial,
a integer,
b integer,
c integer
);
insert into tableA (a,b,c) values (12,34,56);

then,
select id from tableA where (a||b||c)=123456;
in postgresql version 8.2.11,it works.
but in postgresql version 8.3.6,the error as bellow:
ERROR: operator does not exist: integer || integer
LINE 1: select id from tableA where (a||b||c)=123456;
^
HINT: No operator matches the given name and argument type(s). You
might need to add explicit type casts.

is it a bug in 8.2.11 or I install 8.3.6 not completely?