import_from_csv() may delete uploaded files

[magiraud]

Dear all,
The import_from_csv() code contains the following lines :

   # create new id until we get the same as old_id+offset
   while curr_id < csv_id+id_offset[self._tablename]:
         self._db(self._db[self][colnames[cid]] == curr_id).delete()

Inserted records can thus be removed several times before they reach their final id. If there is in the record any upload field, this will trigger delete_uploaded_files(), removing files when autodelete is set.