1.0.28.64: more DIRECTORY work

1.0.28.64: more DIRECTORY work

 * While DIRECTORY on local UNC paths worked as of 1.0.28.61, turns
   out Windows network shares don't exist as far as stat() is
   concerned -- and hence using the proper share path didn't work.
   Replace QUERY-FILE-SYSTEM in MAP-DIRECTORY with UNIX-REALPATH
   sans stat, and we're good.

 * Canonicalize the pathnames for DIRECTORY, so that (DIRECTORY #P".")
   is equivalent to (DIRECTORY #P"./") -- ditto for #P".." and
   #P"../". Also make DIRECTORY treat :UNSPECIFIC names and types as
   if they were NIL.