be digging itself deeper into a hole, it forks off a subprocess
that locates files with too many discontinuities and rewrites them, if
there is enough room.
Optionally the user can manually coaleasce files by running with "-c".
The recent change to lfs_markv is required for the coalescer to do anything.
All of "digging itself deeper", "too many discontinuities", and "enough room"
need to be better defined.
Let lfs_cleanerd record its pid in /var/run like other daemons. Make
mount_lfs not start another cleaner when updating the mount, unless it is
being upgraded from read-only to read-write; when downgrading to read-only,
kill the cleaner using the recorded pids.
lukem