S9 LIB  (dirname string)  ==>  string

Return the directory part of the Unix path name in STRING. Note
that DIRNAME performs merely a syntaxical operation without any
regard to the actual file system structure, i.e.

      (dirname "/foo/bar")  ==>  "/foo"

even if "bar" is also a directory. DIRNAME also takes care of
trailing slashes and recognizes some special cases (see examples).

(dirname "/foo/bar/baz")  ==>  "/foo/bar"
(dirname "foo/bar")       ==>  "foo"
(dirname "foo/bar/")      ==>  "foo"
(dirname "/foo")          ==>  "/"
(dirname "/")             ==>  "/"
(dirname "foo")           ==>  "."
