PR#6054: add support for M.[ foo ], M.[| foo |], etc.
    
    (Patch by Kaustuv Chaudhuri)
    
    The following are now supported:
    
      M.[ foo ]     abbreviation for   M.([ foo ])
      M.[| foo |]         "       "    M.([| foo |])
      M.{ foo }           "       "    M.({ foo })
      M.{< foo >}         "       "    M.({< foo >})
    
    git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14431 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02