This reverts commit 6c182dd14dea6a68dd80e780c763b76dfceae0a2.
No reason to drop working code, for which there is no other alternative
(in this case, formatting/checking HFS+ filesystems).
This reverts commit d0dcad3b91212179a27987ad17b1cbbfceb71a9a.
diskdev_cmds is now packaged as darwin.diskdev_cmds. Linux support is
unknown right now (but PRs are accepted).