Bug 14655: Add a warning if the checkin will fail

Bug 14655: Add a warning if the checkin will fail

On the checkin and checkout page, the checkin will fail if the patron
has requested the privacy and the AnonymousPatron is not correctly set.

This patch adds a warning message on both pages.

Test plan:
0/ Be sure you don't have any patron with privacy=2 (Never)
1/ Set OPACPrivacy, not AnonymousPatron
2/ Go on the checkin, you should a warning (same as before this patch).
3/ Set the privacy=2 for a patron
4/ Go on the circulation page, a warning should appear (for this
specific patron)
5/ Check an item out to this patron
6/ Check the item in on the checkin page.
The item is not checked in and you get a specific message for this
patron.

Confirm other/correct situations don't trigger the messages.

Followed test plan. Works as expected.
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>