Terminates a transaction and undoes all changes that have been
    made to the database since the program's most recent START_
    TRANSACTION statement. The ROLLBACK statement also closes all
    open streams and releases all locks. The ROLLBACK statement
    affects both data manipulation and data definition statements.

    Example:

    RDO> START_TRANSACTION READ_WRITE
    RDO> DEFINE FIELD LOCATION_CODE DATATYPE TEXT SIZE 5.
    RDO> ! Oops, wrong size!
    RDO> ROLLBACK
    RDO> START_TRANSACTION READ_WRITE
    RDO> DEFINE FIELD LOCATION_CODE DATATYPE TEXT SIZE 7.
    RDO> COMMIT