Bug 10942: (QA followup) make warnings to to STDERR

Bug 10942: (QA followup) make warnings to to STDERR

As noted by Robin, STDOUT is used by the script to communicate with
debconf and, hence, the warning messages should be directed to STDERR.

This patch does that. To test:

- Set AUTOMATIC_TRANSLATIONS_UPDATE="no" so the warning normally shows
- Redirect STDOUT to /dev/null:
  dpkg -i koha-common...deb > /dev/null
=> Warning message doesn't show (i.e. it is sent to STDOUT)
- Apply the patch, rebuild package
- Redirect STDOUT to /dev/null:
  dpkg -i koha-common...deb > /dev/null
=> Warning message shows (i.e. is correctly sent to STDERR)
- Redirect STDERR to /dev/null:
  dpkg -i koha-common...deb 2> /dev/null
=> Warning message doesn't show
- Verify that previous tests pass

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>