Bug 18349: SCO - Do not trust the confirmed flag

Bug 18349: SCO - Do not trust the confirmed flag

The "confirmed" flag is used to know if that user confirmed a situation
that needs a confirmation.
But if the issue/renew is impossible the CanBookBeIssued and the
'impossible flags' should be checked.

Otherwise a patron can checkout and renew bypassing the circulation
rules (Understand 'no limit' here...)

Test plan:
Want to renew?
Checkin $barcode, then
/cgi-bin/koha/sco/sco-main.pl?patronid=$cardnumber&barcode=$barcode&confirmed=1&op=checkout

Want to bypass the checkin?
Same url...

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>