Bug 13868: Correct formatting of date on routing list slip

Bug 13868: Correct formatting of date on routing list slip

The date planned printed on the issue slip is not formatted
according to the dateformat system preference setting.

To test:
- enable RoutingSerials
- create a subscription
- create a routing list from the serial collection page
- use the 'print list' links next to the issues to print a routing list
- verify that the date there is not displayed according to the dateformat
  system preference without the patch, but is correct with the patch applied

Followed test plan, date appears according to the date format syspref.
Signed-off-by: Marc Veron <veron@veron.ch>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>