move code from pervasives.ml to camlinternalFormat.ml
    
    This simplifies the charset-handling code, as camlinternalFormat is
    allowed to depend on Bytes and String instead of re-importing the
    needed primitives.
    
    git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14837 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02