Issue: PATHNAME-SUBDIRECTORY-LIST (Version 4)

[Kent M Pitman <KMP@STONY-BROOK.SCRC.Symbolics.COM>]

Please see the issue writeup for PATHNAME-EXTENSIONS which I'm mailing out to
X3J13 in a little while.  I think it is the correct way to deal with
`[not] precluding extensions.'  It basically allows us to establish a model
for how CL pathnames work, and then to selectively violate that model in a
way that is detectable by portable programs. My hope is that it will allow
you to vote in favor of the PATHNAME-SUBDIRECTORY-LIST proposal in some form
(and perhaps other pathname proposals as well) without worrying that it's going
overly constrain you for some idiosyncratic feature that you wanted but couldn't
get group approval for.