Issue: PATHNAME-SUBDIRECTORY-LIST (Version 6)

[Kim Barrett <IIM@ECLA.USC.EDU>]

Yes.  For current practice, IIM does something similar.  The keywords are
different, and only :BACK supported.  I believe the keyword mapping is

  :ABSOLUTE	:ABSOLUTE-DIRECTORY
  :RELATIVE	(no leading keyword)
  :BACK		:SUPER-DIRECTORY

The addition of the :RELATIVE keyword is probably cleaner, since it means that
there is always a keyword at the head of the list, and a test for a relative
directory is (eq (car directory) :relative) rather than something like
(and directory (not (symbolp (car directory)))).

The interaction between :BACK and :WILD-INFERIORS doesn't seem clear.  I
believe this is a case where :BACK and the thing preceding it cannot be
spliced out (you can end up with (... :WILD-INFERIORS :BACK ...).  Also,
(:ABSOLUTE :BACK ...) should probably signal an error.