Bug 14418 : More XSS vulnerabilities in opac-shelves.pl

Bug 14418 : More XSS vulnerabilities in opac-shelves.pl

To test:
1/ Hit a url like
/cgi-bin/koha/opac-shelves.pl?viewshelf=7&op=modif&display="><script>alert('oh
noes')</script>  Where the id is a valid shelf id
2/ Notice the js is executed
3/ Apply patch
4/ Reload page
5/ Notice input is now escaped on display

Signed-off-by: Jonathan Druart <jonathan.druart@koha-community.org>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Tested in Debian, couldn't reproduce the alert in Iceweasel, but in
Chromium. Patch fixes it.