S9 EXT  (sys:getgrnam string)   ==>  alist
        (sys:getgrgid integer)  ==>  alist

Return the group record for the group name STRING or the group ID
INTEGER. The returned association list has the following members:

        ((name . string)    ; group name
         (gid  . integer))  ; group ID

(sys:getgrnam "staff")  ==>  ((name . "staff") (gid . 20))
(sys:getgrgid 0)        ==>  ((name . "wheel") (gid . 0))
