If $HOME isn't canonical (e.g. on FreeBSD it's /home/user while the
canonical path is /usr/home/user), replacing the canonical version of $HOME
with $HOME means that we'll read back a different value than we wrote
in.
It might seem "equivalent" but it leads to surprises like
KRecentDocuments showing duplicates because /usr/home/user became
/home/user in the KConfig roundtrip (but not in the XBEL roundtrip).
This commit loses the replacement of /usr/home/user with $HOME on
FreeBSD, but I think an exact roundtrip is what we expect, rather than
stuff being modified under our feet. The alternative would be to
canonicalize everything in KRecentDocuments but users don't want to
see the /usr in front, I assume (so we would have to use a cache of
canonicalized path, for the removal of duplicates, awful performance
wise).