Bug 797521 - Receivable Aging (beta): prepayments logic doesn't work, appears to use incorrect absolute value logic

Overpayments create at least 2 APAR splits (1 for each invoice, and 1
for the overpayment), they were processed multiple times.

Modify query to return unique transactions, thereby ensuring a payment
gets processed once only.

gnucash/report/business-reports/new-aging.scm

@@ -235,7 +235,7 @@ exist but have no suitable transactions."))
 
      (else
       (setup-query query accounts report-date)
-      (let* ((splits (qof-query-run query))
+      (let* ((splits (xaccQueryGetSplitsUniqueTrans query))
              (accounts (sort-and-delete-duplicates (map xaccSplitGetAccount splits)
                                                    gnc:account-path-less-p equal?)))
         (qof-query-destroy query)