Really remove debug output.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14446 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
#5779: adopt gasche's sentinel solution.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14447 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02