Don't resolve references between stop comments

[Julow]

In this example, the comment containing the reference and the target of the reference are "removed" from the documentation with stop comments:

(** . *)

(**/**)

val x : int

(** {!x} *)

(**/**)

Odoc attempts to resolve the reference but fails, which result in unfixable warnings.

[Julow]

This no longer result in a warning since recent changes to hidden paths.
References are still being resolved:

(** . *)

(** {!x} *)

(**/**)

val x : int

(** {!y} *)

(**/**)

The reference {!x} resolves, and result in an anchor to #val-x which is wrong. Reference {!y} results in an error.