New -strict-formats flag to detect and fix invalid formats
    
    (Request by Mark Shinwell, ack'ed by Damien Doligez)
    
    git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@15138 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02