Attributes and extension points in class_expr.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13500 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Extension nodes and attributes for class types.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13501 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Extension nodes as class field or class type field.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13502 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Cosmetic.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13503 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
TODOs.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13504 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02