Bug 10915: (QA followup) warn if cannot read history.txt

Bug 10915: (QA followup) warn if cannot read history.txt

This patch makes about.pl test if success opening history.txt, and
shows a convenient warning to the end user. No more warnings in the logs
(about.pl: readline() on closed filehandle $file at /usr/share/koha/intranet/cgi-bin/about.pl line 166)
and better problem solving information for the end user.

Sponsored-by: Universidad Nacional de Cordoba
Signed-off-by: Galen Charlton <gmc@esilibrary.com>