Use [%lid expr] syntax for extensions.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13345 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Extension as structure/signature items [%%lid expr].

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13346 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Allow to put 'item' attributes before the 'type' or 'module rec' keywords.  They apply to the first item in the declaration.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13347 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02