Bug 24313: Always display XSLT errors in logs

Bug 24313: Always display XSLT errors in logs

From
  commit 295ae33800a322facfdf56795f4c02b2fd53432b
  Bug 20272: Replace error numbers by codes in XSLT_Handler

"""
    Make XSLT_Handler a little bit less noisy by defaulting print_warns to
    false unless $ENV{DEBUG} is set. (See also bug 19018).
"""

I think we should warn the errors in the logs. They are not debug messages here, we should not rely on DEBUG.
If too noisy we should fix the original issues, not hide all the errors (which make the XSLT debugging super hard)

Test plan:
Break a XSLT, reload the page and confirm that there are useful errors in the Koha log file

Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>