AddLine()

          Adds a divider line to a submenu as a non-selectable item

    Syntax:

         AddLine( aMenu, nSubMenu [, nPos] ) -> Nil

         aMenu    : The menu created with NewMenu()
         nSubMenu : The number of the submenu to which the
                    divider line is to be added
         nPos     : The position of the divider line in the submenu;
                    last position if not specified

    Description:

         Adds a divider line to a submenu, setting it as non-selectable.

    Return:

         Nil.

    Example:

         aMenu := NewMenu( { "^System", "^Tools", "^Other" }, ;
                           { "N/W", "R/W", "W/B",  "W+/B", ;
                             "N/W", "W/B", "N+/W", "R/W", "GR+/B" } )
         AddItem ( aMenu, 1, "Item ^1", "Message 1" )
         AddItem ( aMenu, 1, "Item ^2", "Message 2" )

         AddLine ( aMenu, 1, 2 )  // add a line between two items.