wn_save -- save screen image 

        USAGE

          wn = (WINDOWPTR)wn_save(page, row, col, width, height)
          int page, row, col, width, height;

                page -  always 0.
                row  -  row of upper left hand corner of the window
                col  -  column of upper left hand corner of the window
                width - INSIDE dimension (max value is 78)
                height- INSIDE dimension (max value is 23)

          wn_save can be used to save areas of the screen for purposes
          other than windows.

          Memory for the screen image is dynamically allocated.

        RETURNS

          wn = window handle or NULL if error

        CAUTIONS

          The window handle returned by wn_save should only be used with
          wn_restore, use with other routines could produce unpredictable
          results.