Make Parsetree more uniform by keeping locations in all records which have attributes.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14659 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
More precise location on 'name must be unique' error (report the identifier name instead of the whole declaration).

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14660 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02