mconf/nconf: mark empty menus/menuconfigs different from non-empty ones

Submenus are sometimes empty and it would be nice if there is
something that notifies us that we should not expect any content
_before_ we enter a submenu.

A new function menu_is_empty() was introduced and empty menus and
menuconfigs are now marked by "----" as opposed to non-empty ones that
are marked by "--->".

This scheme was suggested by "Yann E. MORIN" <[email protected]>.

Signed-off-by: Dirk Gouders <[email protected]>
Tested-by: "Yann E. MORIN" <[email protected]>
Reviewed-by: "Yann E. MORIN" <[email protected]>
Signed-off-by: "Yann E. MORIN" <[email protected]>
4 files changed