rtn1_trans name clash

Version

The Coq Proof Assistant, version 8.6 (December 2016)
compiled on Dec 29 2016 23:38:14 with OCaml 4.02.3

However, the issue is probably present in the latest version ( 8.7.2) as well
[edit: fails on current master too]

Operating system

Debian Linux

Description of the problem

This is a reopen of issue coq/coq#2152. The name clash is still present
in Relations. While rtn1_trans was renamed to clos_rtn1_rt in
Relations/Operators_Properties.v but it was re-added as a notation at the end
(at line 435). The notation is not visible in the documentation.
Code to reproduce the bug:

Require Import Relations.

Lemma rtn1_trans_test1 A R x y z (Ht:clos_refl_trans_n1 A R x y) (H1:R y z):
  (clos_refl_trans_n1 _ R x z).
Proof.
  (*The fully qualified name works*)
  eapply Coq.Relations.Relation_Operators.rtn1_trans; eauto.
Qed.

Lemma rtn1_trans_test2 A R x y z (Ht:clos_refl_trans_n1 A R x y) (H1:R y z):
  (clos_refl_trans_n1 _ R x z).
Proof.
  eapply rtn1_trans; eauto. (*Fails*)
Qed.

Inspect Relations/Operators_Properties.v around the notation near line 435, then run the two Coq lemmas in the issue to confirm the qualified and unqualified behavior. Done means the rtn1_trans name clash is resolved and the reproduction no longer fails; add or update a regression test if the surrounding test structure supports it.