menuconfig: Add "breadcrumbs" navigation aid

Displays a trail of the menu entries used to get to the current menu.

Signed-off-by: Benjamin Poirier <bpoirier@suse.de>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
[yann.morin.1998@free.fr: small, trivial code re-ordering]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>