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

[Stefan Monnier]

> I confirm that it prevents `where-is-internal` from calling 
> `context-menu-map`,
> and everything else works fine, but I'm not sure how this change fits
> into the overall design of the menu bindings.  Maybe, `make-sparse-keymap`
> means that `context-menu-entry` contains an empty menu initially.

No, it's just that `where-is-internal` by-and-large doesn't run the
`:filter`s when doing its search, so instead of seeing a binding to
`ignore` it will see a binding to an empty keymap.

As we've seen `where-is-internal` does end up running the `:filter`
sometimes, but it's only done on those few bindings that match.

When building a menu, the `ignore` or the empty keymap won't be used at
all (their only use will be to pass them to the `:filter` function,
which ignores that argument).  That's why the "binding" is currently
called `ignore`: not because we want to use the `ignore` command but as
a way to say "this is not used".


        Stefan