Bug 10445: make SIP Server respect maxoutstanding system preference

Bug 10445: make SIP Server respect maxoutstanding system preference

The system preference 'maxoutstanding' is defined as the maximum amount
of fees owed by the patron before Koha should block placing holds (
terrible naming on this one ).

However, although the Koha OPAC respects this preference, placing holds
via a SIP2 device will not.

Test Plan:
1) Set maxoutstanding to $10
2) Pick a patron owning more than $10 in fees
3) Attempt to place a hold for this patron from a SIP2 device
   This attempt should succeed
4) Apply this patch
5) Restart your SIP2 server
6) Attempt to place a hold for this patron from a SIP2 device again
   This attempt should now fail

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>