tw_ScrApp( scrpos, scr1, scr2, leng, wid )
 ----------------------------------------------------------------------------
     Append a screen line to a Clipper Savescreen variable.

       Arguments:

     scrpos - 'C' "T", "L", "B", "R" for: top, left, bottom or right of
                  the present screen.

     scr1   - 'C' SAVESCREEN() to append.

     scr2   - 'C' SAVESCREEN() to append to.

     leng   - 'N' Length of screen to append to.

     wid    - 'N' Width of screen to append to.

       Return:

     Clipper SAVESCREEN() variable.

       Example:

     tw_ScrApp( "T", Scrn1, Scrn2, len, wid + 1 )