Bug 23074: Holds table sort does not understand dateformat

Bug 23074: Holds table sort does not understand dateformat

Holds table does not sort correctly when the dateformat is eg. DD.MM.YYYY.

Test plan:
1) Create multiple holds for a patron with different hold creation
   and expiration dates, with different years, months and days.
2) Change the dateformat to DD.MM.YYYY.
3) Resort the holds table (in circ/circulation or members/moremember)
   by the hold date or expiration date.
   The table sorts the date by the day number.
4) Apply patch
5) Redo 3 - the table now sorts correctly.

Signed-off-by: Pasi Kallinen <pasi.kallinen@koha-suomi.fi>
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Arthur Bousquet <arthur.bousquet@inlibro.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>