Importing Equations breaks std++'s 'simplify_eq' tactic

[RalfJung]

This is a re-filing of #449, which apparently has not actually been fixed yet.

The bug is demonstrated by the following proof script:

Module Import tactics.
  Tactic Notation "simplify_eq" := idtac.
End tactics.

(* Our new tactic works just fine here. *)
Goal True. Proof. simplify_eq. auto. Qed.

From Equations Require Import Equations.

(* Importing Equations has broken our tactic. *)
Goal True. Proof. simplify_eq. auto. Qed.

This is with version 1.3.1+8.20 of the opam package.