Bug 10731 - IntranetSlipPrinterJS is not working for hold slips [v3.10/v3.12]

Bug 10731 - IntranetSlipPrinterJS is not working for hold slips [v3.10/v3.12]

Hold slips aren't printing automatically with JS Print Setup because it
appears the system preference IntranetSlipPrint is never being passed to
the template.

Test Plan:
1) Set up JSPrintSetup
   http://wiki.koha-community.org/wiki/Setting_up_slip_printer_to_print_silently
2) Place a hold
3) Check the item in to capture the hold
4) Click "Print and confirm"
5) Note the slip does not print automatically
6) Apply this patch
7) Repeat steps 2 through 4
8) Observe that the slip now prints automatically

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Tested successfully in 3.10.x and 3.12.x

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>