Fix PR#6465: allow incremental weakening of module aliases

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@15405 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
The path under Tpackage doesn't refer to a type path (but to a module type path).

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@15409 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Sync with trunk.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/constructors_with_record4@15410 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02