PR#5547: Enable the "-use-ocamlfind" option by default

ocamlfind library management has been around for while and is
considered to be installed by default on any OCaml system. Therefore
it's safe to assume that the default behavior of ocamlbuild should be
to use new ocamlfind support normally enabled explicitly by
-use-ocamlfind flag. The -use-ocamlfind flag has now a status of
depreceation and instead new flag -no-ocamlfind causes ocamlbuild to
not try to use new set of parametric tags for supporting ocamlfind.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13938 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02