Factotum used to mount itself on /mnt and serving the first-level
directory "factotum" itself. This has the undesired consequence
that it has to respond to all walks crossing the /mnt directory.
Instead, we make factotum interpret the previously ignored
mount-spec (aname). If it is "factotum", it serves the
factotum directory as the root, so it can be directly mounted
onto /mnt/factotum. For backwards compatibility, the old
behaviour is preserved.
The namespace file will now always mount factotum onto /mnt/factotum.
In the case of a old factotum, that ignores the mount-spec,
do a bind moving /mnt/factotum/factotum to /mnt/factotum.
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