Bug 11341: fix XSS bug in opac-search.pl (facets)

Bug 11341: fix XSS bug in opac-search.pl (facets)

This patch fixes the prog theme; the bootstrap theme already
does the necessary filtering.

To test
1/ Craft a url like
 cgi-bin/koha/opac-search.pl?idx=kw&q=fish&offset=20" onmouseover%3dprompt(994000) bad%3d"
 (the search must return enough results to have a show more link in the facets)

2/ Check the source, or mouseover the Show more links in the facets
   Notice the code is executable

3/ Apply patch - notice it is no longer executable

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>