Bug 5995 Follow up: variable scope in koha/sco/sco-main.pl

Bug 5995 Follow up: variable scope in koha/sco/sco-main.pl

The patronid value (cardnumber) set by checkpw in the case of SelfCheckoutByLogin
was improperly scoped with 'my' inside a conditional.  The changes followup to 5995
made this more apparent, causing logins to fail.

Also added "parts copyright" statement to the script, since ByWater Solutions did make some
significant contributions to the operations of the page

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>