twClear( wBorder, wFill, wT, wL, wB, wR)
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     Clears or fills a region within the active window in the current
     window colour, including or excluding the border.

       Arguments:

     WBorder  - 'L' .T. to include the border, .F. to exclude in either
                    a box or a window.  Defaults to .T.

     wFill    - 'C' Fill Character. Defaults to " ".

     wT,wL
     wB,wR   - 'N' Relative Window Coordinates. This defaults to
                   display area for the current window if not passed.

       Return:

     Current window handle

       Example:

     twClear( .T., "#", 12, 7, 18, 31 )

     Clears a box with chr(177) including the border.