1.0.30.49: delete-file behaviour reversal
In the 1.0.29.x series, DELETE-FILE started deleting the truename of the
given pathname designator (rather than the pathname itself), meaning
that symlinks could no longer be deleted. Revert back to the historical
behaviour. (Noted on sbcl-devel by Luis Oliveira 2009-08-18.)
Although the behaviour hasn't changed recently, there's a similar issue
in RENAME-FILE, but that operator has such bizarre behaviour anyway it
might be worth just letting sleeping pathname functions lie.