allow for sequence mismatches between cross-referenced sequence records according to variant and splice-variant annotation

Occasionally, there are mismatches between the same sequence as reported by different databases.
e.g. https://www.uniprot.org/uniprot/P08411

which is cross-referenced by its ENA CDS entry: https://www.ebi.ac.uk/ena/browser/api/embl/X04129.1?lineLimit=1000

The mismatched sequence will prevent CDS cross references being created for the protein retrieved from Uniprot, and also prevent Uniprot annotation from being added directly to the ENA protein product (after retrieving X04129 from ENA and applying 'Calculate -> show crossreferences -> EMBLCDSPROTEIN' ).