Ensure that delayed checks are run in the proper warning configuration (so that the warnerror attribute applies, in particular).

git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@14863 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Document bad interaction between ppwarning and warning/warnerror attributes.

git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@14864 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02