More uniform syntax:

Attributes:
  expr (:foo expr)
  type (:foo expr)
  str_item ..(:foo expr)

Extension nodes:
  expr (&foo expr)
  type (&foo expr)
  str_item ..(&foo expr)




git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13331 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02