Fails with assertion on nested modules

[andy-morris]

With the following files:

(* a.ml *)
module type S = sig
  module M: sig end
end

(* b.ml *)
module type S =
  [%import: (module A.S)]

I get the error "File "src/ppx_import.cppo.ml", line 313, characters 9-15: Assertion failed".

(This is with the version 1.4 currently in opam for compiler version 4.06.0.)

[xguerin]

Related to #20. Closing this entry. I'll look into it.