make DELETE-FILE respect *DEFAULT-PATHNAME-DEFAULTS*
MERGE-PATHNAMES to get an absolute pathname. (Using TRUENAME would be wrong,
since then we would delete files pointed to by symbolic links, and not the
symbolic links themselves -- a nasty regression that would be!)
Also remove the "for error checking" TRUENAME call from there: unlink will
give us an errno that tells what we need to know -- and lo! there is one
race condition less in the system.
Previously using relative pathnames it was possible to accidentally delete
the wrong file.
NB: currently DELETE-DIRECTORY and RENAME-FILE use TRUENAME with just the
aforementioned unfortunate consequence, but I'm hesitant to change them
during the freeze -- so dealing with this issue in them will have to
wait a bit.