Bug 19569: Set X-Frame-Options=SAMEORIGIN - opac-showmarc.ok

Bug 19569: Set X-Frame-Options=SAMEORIGIN - opac-showmarc.ok

Before and after:
wget 'http://catalogue.kohadev.org/cgi-bin/koha/opac-showmarc.pl?id=1&viewas=html'
must be the same

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit 727f915c1b2e2ee7869d14d852b48eeaa67735ae)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>