S9 EXT  (sys:user-name integer|string)   ==>  string
        (sys:user-uid integer|string)    ==>  integer
        (sys:user-gid integer|string)    ==>  integer
        (sys:user-gecos integer|string)  ==>  string
        (sys:user-home integer|string)   ==>  string
        (sys:user-shell integer|string)  ==>  string

Return a specific member of the user database entry for the
given user. A user may be indicated by its user name (STRING)
or UID (INTEGER). See SYS:GETPWNAM for details. Basically
(sys:user-MEMBER user) is short for:

        (let ((u (if (string? user)
                     (sys:getpwnam user)
                     (sys:getpwuid user))))
          (if u
              (cdr (assq 'MEMBER u))
              (error "no such name or UID")))

(sys:user-gecos "man")  ==>  "Mr. Man Pages"
