Get rid of some uses of implicit removal of optional arguments.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14497 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
#6352: add a warning on implicit removal of optional arguments.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14498 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02