Obtaining the names of all local variables

[Bart Schaefer <schaefer@brasslantern.com>]

Oliver mentioned:
> I did something like the following in _git recently. It works
>   arr=( one two three )
>   local $arr

This got me thinking, wouldn't it be helpful if zsh/parameter had an array
$locals that holds the names of all the local parameters?  Then you could

    needs_private_scope() { local -h $locals; ... }

It then occurred to me that it might be more natural to have "local" handle
this.  But:

torch% () { local +m \* }
(anon): bad option: -m

Of course there's an ambiguity in both cases; given

    typeset bar
    scope1 () {
        local foo
    }
    scope2 () {
         local foo bar
         scope1
    }

Should "bar" be considered local in scope1 when called from scope2?  If not,
this whole idea is somewhat moot; you'd need a way to select which scope
you want to know all the locals in, which is ugly to contemplate.