Bug 38125: Add a warning if privacy pulldown is changed to "never"

Bug 38125: Add a warning if privacy pulldown is changed to "never"

It is possible to interpret the language on opac-privacy.pl as only
acting on future checkins and not current historical checkouts. We
should add clarifying text to that page

Test plan:
1) Apply this patch
2) Enable opac privacy
3) Change pulldown to "never"
4) Note the warning message appears

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>