* Adapt lfs_cleanerd to use the fcntl call to get the Ifile filehandle,
so it need not be in the namespace.
* Make lfs_cleanerd be more careful when there are very few available
segments.
* Remove the Ifile from the filesystem namespace. The cleaner now uses
a fcntl call on the root inode to find the Ifile filehandle.
* Make lfs_cleanerd less verbose when the filesystem is unmounted.
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