Check for duplicate credit memos

SAP Notes: 305277

If you want to check when you enter credit memos whether a
corresponding credit memo has already been entered,
implement the modification proposal from the SAP Note.
The changes are not delivered by Support Package and are
not included in the standard system.

The modifications in the modules ‘DUPLICATE_INVOICE’ and
‘DUPLICATE_INVOICE_HEADER’ are valid for conventional
invoice verification up to and including Release 46B.
The modification in the function module ‘MRM_DUPLICATE_INVOICE_CHECK’
is valid for the Logistics Invoice Verification.