twScBarUpdate( _SBar, rCurrent, rTotal,;
                sForceUpdate )
 ----------------------------------------------------------------------------
     Updates the display of the scroll bar tab IF the position has
     changes OR you request it.

       Arguments:

     _sBar        - 'A' Scroll bar array.

     rCurrent     - 'N' Current record or array element.

     rTotal       - 'N' Total records or elements.

     sForceUpdate - 'L' Flag to force the display to be updated even if
                        position is not changed.

       Return:

     Bar number.

       Example:

     twScBarUpdate( nBar, nCurrent, RecLast, .T. )