wn_dborder -- draw (replace) border on window

        USAGE

          wn_dborder(wn, ul, ur, tb, sd, ll, lr);
          WINDOWPTR wn;
          int ul, ur, tb, sd, ll, lr;

            wn - window handle
            ul - upper left corner character
            ur - upper right corner character
            tb - top/bottom line character
            sd - left/right side character
            ll - lower left corner character
            lr - lower right corner character

          The currently defined border attribute is used when drawing the
          border.

        RETURNS

          TRUE or NULL if error

        CAUTIONS

          The window "wn" automatically becomes the top window tile upon
          return.
.