Better representation of variance in the Parsetree.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13474 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Generate a variantizer object, allowing to hook custom behavior.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13475 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
AST printer based on lifting.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13476 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02