Bug 18317: Allow check out of already checked out items through SIP

Bug 18317: Allow check out of already checked out items through SIP

This patch allows checkouts to be processed via SIP even when
the item is already checked out to a user.

Test plan:
0) Apply the patch
1) koha-sip --stop kohadev
2) koha-sip --start kohadev
3) misc/sip_cli_emulator.pl -a localhost -p 6001 -l CPL -su term1 -sp term1 -m checkout --patron koha --item 39999000001310
4) misc/sip_cli_emulator.pl -a localhost -p 6001 -l CPL -su term1 -sp term1 -m checkout --patron 23529000035676 --item 39999000001310
5) Note the output includes "AFItem checked out to another patron"
6) Enable system preference "AllowItemsOnLoanCheckoutSIP"
7) misc/sip_cli_emulator.pl -a localhost -p 6001 -l CPL -su term1 -sp term1 -m checkout --patron 23529000035676 --item 39999000001310
8) Note the output no longer includes "AFItem checked out to another patron" and the item has been checked out to patron 23529000035676

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>