Experimenting with alternative syntax for extension nodes (as an annotation on the opening keyword/delimiter).

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13378 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Adapt examples.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13379 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Adapt examples.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13380 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02