bug#9923: 24.0.91; `where-is' does not find recentf menu items (cmds, not files)

[Stefan Monnier]

> `where-is-internal(ignore)` raises its ugly head again:
>
> 0. emacs -Q
> 1. M-x TAB
>
> Debugger entered--Lisp error: (void-function cl--set-substring)
>   cl--set-substring(#("*scratch* x" 0 9 ...
>   tab-bar-auto-width(((sep-1 menu-item " " ignore) (current-tab menu-item 
> #("*scratch* x" 0 9 ...
[...]
> But using `make-sparse-keymap` fixes it again:

Yay!

But we should also fix the `cl--set-substring` error there.


        Stefan