For %{..%}, restore Pierre's semantics
    
    (printf {%foo%} bar) will print the string representation of the
    format type of both `foo` and `bar`, instead of printing `bar`
    (for this purpose one can just use %s). `bar` content is ignored, but
    the typer should check that its type is compatible with the one of
    `foo`.
    
    This semantics allows to use (printf %{..%}) for testing/debugging the
    use of %(...%): put in the brackets what you believe to be the format
    type you want to use, and as argument the format you wish to pass, and
    you'll get type-checking confidence and the "canonical" representation
    of the format string which you can use in the %(...%) -- note that
    using the canonical format type is not mandatory.
    
    git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14840 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02