.Scroll function.
      Edit/Browse panel is scrolled both direction, directory list and
      filename input panel is scrolled vertical only.
      Scroll unit of filename input panel is fixed to page-size.
      Key usage to scroll screen is as following.

      Direction arrow key(Up/Down/Left/Right)
        Screen is not scrolled even when cursor reached to the edge of screen as default.
        If FREECSR mode is set OFF by OPT command("OPT freecsr off"),
        scroll occurs at the edge of screen by the unit of half of page size.
        If keyboard is in the status of ScrollLock on, scroll unit is 1 line/column.
      Shift+Up/Down
        Vertical scroll by one line.
      PgDn/PgUp
        Vertical scroll by the unit of value in the scroll-size field
        on the 2nd line. The field is over-writable and valid value is
        PAGE, HALF, CSR, MAX, numeric-value. CSR means scroll to move the line/column
        of the current cursor position to the edge of screen.
      F10/F11(this function key assignment is changeable)
        Horizontal scroll by the value of scroll-size field.
      Shift+PgDn/PgUp
        Jump to Top/Last page of the file.
      Others.
        Shift+Right/Left is to display End/Top column of the line.
        It may cause scrolling.
        Input on the right edge of file edit screen cause to scroll
        to the right by the unit of HALF.

#if defined(WXE) || defined(LNX)
      Using mouse.
        Wheel of mouse scrolls vertically, Shift+wheel scrolls horizontally
          and Ctrl+wheel jumps to the top/last page of file.
        wxe support tile wheel mouse to scroll horizontaly by tilting
          the middle button.
#endif