Some tactics fail if traverse function is anonymous

[KevOrr]

E.g.

Inductive term : Set :=
| ...
.

Instance Traverse_term : Traverse term term :=
  {traverse := (fix rec f l e := ...)}.

Goal @TraverseFunctorial term _ term _.
Proof.
  constructor. prove_traverse_functorial.

Shown to break:

• prove_traverse_functorial
• prove_traverse_relative
• prove_traverse_var_is_identity

Shown to work:

• prove_traverse_var_injective
• prove_traverse_identifies_var