Bug 12923 Improve error logging for advance_notices.pl

Bug 12923 Improve error logging for advance_notices.pl

Show borrowernumber when no letter of type is found and force utf8
output when running advance_notices.pl with -n flag, diacritics run awol
in the console output!

Also when debugging which borrower requests undefined letter templates,
it is very handy to log the borrowernumber so we catch and fix bad
borrower message transport settings.

TEST PREPARATION:

0. Edit the ODUEDGST letter, find an undefined letter for any trasport
   type.

::TESTS ARE (ALMOST) THE SAME AS IN bugg 12922::
TEST PLAN:

1. Find a borrower and from the messaging preferences set the "Advance
   notice" transport type to the undefined digest. Set the "Days in
   Advance" to 1.
2. Check-out something for that borrower and set the due date for
   tomorrow.
3. Run "misc/cronjobs/advance_notices.pl -c -n -v" from the terminal.
4. BEFORE THIS PATCH: You get an error "no letter of type 'PREDUEDGST'
   found. Please see sample_notices.sql at ./advance_notices.pl line
   366."
4. AFTER THIS PATCH: You get an error "no letter of type 'PREDUEDGST'
   found for borrowernumber 1104659. Please see sample_notices.sql at
   ./advance_notices.pl line 368."
   Makes life more worth living for!
   Also diacritics printed on screen are displayed properly.

Signed-off-by: Frederic Demians <f.demians@tamil.fr>
  I confirm the diacritics issue and solution. borrowernumber is
  displayed with warning when the 'no letter...' message is displayed.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>