(coll, fina, repa, shark, disloan): Fix calculation of regular and

(coll, fina, repa, shark, disloan): Fix calculation of regular and
extended (beyond due date) loan time.  At the due date, or after a
last payment made at the due date, durations were zero in fina() and
unpredictable elsewhere.  With luck, debtors could abuse this to repay
loans cheap (they couldn't gain cash, though), sharks to purchase
loans cheap, and creditors to collect excessively.