set_enum_idx

specify another serial number for a enum
     enum_id - id of enum
     idx     - new serial number.
               If another enum with the same serial number
               exists, then all enums with serial
               numbers >= the specified idx get their
               serial numbers incremented (in other words,
               the new enum is put in the middle of the list
               of enums).
               If idx >= get_enum_qty() then the enum is
               moved to the end of the list of enums.
returns: comment string

success set_enum_idx(long enum_id, long idx);