Bug#320470: Cups does not print to a serial printer

["Marco Antonio V. Assad" <marcova@mg.trt.gov.br>]

Package: cupsys
Version: 1.1.23-10

When we upgraded from woody to sarge, we noticed that our serial printers (we
use a cyclades serial board) stopped working. Raising the debug level in
cupsd.conf from info to debug, we noticed in /var/log/cups/error_log that the
file /usr/lib/cups/backend/serial was missing. 

To solve this issue, we created a symbolic link using the following commands:
  cd /usr/lib/cups/backend
  ln -s ../backend-available/serial .

So after restarting cupsys everything started working normally.