busybox

Move SUSv2 obsolete feature disabling to debug menu, invert meaning of
symbol (switched on to remove now: test your apps to make sure they _don't_
do this, because as some point we should just yank it), fixup head/tail/fold.

Also tweak "make allyesconfig" so anything starting with CONFIG_DEBUG gets
left switched off.  Possibly other things we want to put in the debug menu?