Bug 5371: Force no caching for private pages at the OPAC

Bug 5371: Force no caching for private pages at the OPAC

In order no to slow too much the browsing, it is certainly not a good
idea to add this cache-control value for all pages at the OPAC.

This patch just adds where the author found it could be useful.

Test plan:
1/ Login at the OPAC
2/ Go on the account page (opac/opac-account.pl)
3/ Click log out
4/ Use the back button of your browser
Without this patch you will see the previous page.
With this patch, the previous page will be reloaded and you will be
redirected to the login form.

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>