Improve snapshot mechanism for warning configuration.

git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@14872 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
fix PR#6415: format had forgotten about 'b' boxes

git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@14873 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02