twClearLine( nRow, wBorder, cAttr )
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     Clear a Line in a window, with or without the border.

       Arguments:

     nRow    - 'N' Relative window row.

     wBorder - 'L' Logical to include the border area. This parameter
                   defaults to .F.

     cAttr   - 'C' Clipper Colour Attribute or string.  Defaults to the
                   current window text colour.

       Return:

     Current window handle

       Example:

     twClearLine( 2 )

     Clear the second line in the window to the current window colour,
     excluding the border area.