remove dist/*, now that they're not needed.
if MAKEDEVTARGETS is set, use MAKEDEV.wrapper and makedev2spec.awk to
create an mtree specfile containing the devices that would be made with
"etc/etc.${MACHINE}/MAKEDEV $MAKEDEVTARGETS".
otherwise, copy etc/etc.${MACHINE}/MAKEDEV to dev/MAKEDEV (via list.makedev)
- add mtree.common; contains directories used by all images, and optional
entries for dist/*
lukem