||Marks double entries with regard to an index
||MARKDOUBLES(db : INTEGER; index : INTEGER|STRING [,mode : INTEGER]) : INTEGER
||db : table handle from OpenDB
index : index number or index name
0 (default) // w/o the first record
1 // with the first record
||Number of the found records. Additional the dublicate enties are marked.
Marks all records, that have a identical entries in the given index.
When mode is set to 0 (the default), exactly n - 1 records will be
marked. The very first record (let's say the master record) is not.
For mode = 1, this record is set to marked also. So it is exatly n records that are marked.