Koha::XSLT::Security - Add security features to Koha::XSLT::Base
    use Koha::XSLT::Security;
    my $secu = Koha::XSLT::Security->new;
    $secu->register_callbacks;
    $secu->set_parser_options($parser);
    This object allows you to apply security options to Koha::XSLT::Base.
    It looks for parser options in koha-conf.xml.
    Creates object, checks if koha-conf.xml contains additional configuration
    options, and checks if XML::LibXSLT::Security is present.
Register LibXSLT security callbacks
    my $xslt = XML::LibXSLT->new;
    $security->set_callbacks( $xslt );
    Apply registered callbacks to a specific xslt instance.
    $security->set_parser_options($parser);
    If koha-conf.xml includes koha_xslt_security options, set them.
    We start with implementing expand_entities.
    David Cook, Prosentient Systems
    Marcel de Rooy, Rijksmuseum Netherlands