Infix syntax for attributes/extension nodes restricted to expression constructions starting with a (combination of) keywords.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13419 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Get rid of alternative syntax for '(module...)'.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13420 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02