I think PostgreSQL 8 and that query aren't going to work along.
PostgreSQL different versions in the 8 series handle CONCAT in a something random way. This version, it seems, doesn't allow CONCAT of string literals (in this case '/'). In version 9 it works fine, at least in my experience.
In order to make the code PostgreSQL 8-compatible, it should read
SELECT 'andy@ciordia.info' AS master_user,
mailbox.storagebasedirectory || '/' || mailbox.storagenode || '/' || mailbox.maildir AS home (etc...)
Actually, I think CONCAT() is not a standard SQL function.