Fix OX-5996 SQL stored banners not working on PostgreSQL

> From https://developer.openx.org/jira/browse/OX-5996

It appears that since the separate delivery DALs (mysql.php / pgsql.php) were merged into a single file, a bug slipped in that prevents SQL stored banners from being properly returned when PostgreSQL is used, as there's a missing pg_unescape_bytea() call.