mmenu: separate /pandora/mmenu scan from pnd-scan per se .. so if .desktop is scan, and .pnd is not, but an aux-pnd searchpath is defined
then attempt to pnd-disco there (regardless of .pnd scan being disabled otherwise.) This will restore expected functionality from previous
(pre-.desktop scan) releases, and generalyl will not bother anyone (few use 'mmenu' specific apps anyway.) For people who do use it, it'll
start working again, though not quite as fast as a pure .desktop scan (since there are no .desktop's for the mmenu-specific pnds, by definition.)