JBAS-1588 CC payment balances match active data

JBAS-1588 CC payment balances match active data

Ensure that the total amount to be tracked as payments in EG after a
successfull PayPal payment match the PP payment amount.  Exit early and
return a non-success to PP when the totals don't match.

This imbalance can occur when a transaction is paid by some other client
(secondary PP instance, staff client) after the PP transaction has been
initiated with the original transaction balance owed amount.

IOW, don't accept payments for transactions that were paid off through
some other mechanism while the PP transaction was in process.

Signed-off-by: Bill Erickson <berickxx@gmail.com>