AddItem()

         Adds a selectable item to a submenu

    Syntax:

         AddItem( aMenu, nSubMenu, cItem, [cMess], [nPos], [aSub] ) -> Nil

         aMenu    : The menu created with NewMenu()
         nSubMenu : The number of the submenu to which the item
                    is to be added
         cItem    : The item to add to the submenu
         cMess    : The message text for the item
         nPos     : The position of the item in the submenu;
                    last position if not specified
         aSub     : An array of the submenu options

    Description:

         Adds an item to a submenu, activating the item as 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", , { "Sub1", "Sub2" } )