S9 EXT  (sys:access string integer)  ==>  boolean

Test whether the file named in STRING can be accessed in the
way encoded in INTEGER. INTEGER may have one of these values:

        sys:access-f-ok  test if the file exists
        sys:access-r-ok  test if the file can be read
        sys:access-w-ok  test if the file can be written
        sys:access-x-ok  test if the file can be executed

(sys:access "." sys:access-f-ok)  ==>  true
