Introduce and use higher-level wrappers around parsing routine for .ml/.mli files, taking care of -pp and -ppx preprocessors.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14084 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
More direct style, remove the temporary file created by -pp processor right after it has been read.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14085 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02