list_dialog (was Re: variable existence checking)

[Tony Balinski]

Quoting "A.V.Kuznetsov" <kuzn at umps.mephi.ru>:

> A patch is better than nothing.
> Tony, can you put your patch listDialogKeyWords.diff
> in the Patch Tracker?
> It is stable, I often use it's new helpful features.
> The string entry is very powerful.

The feature this patch provides is indeed very useful, but I don't like the
way I did it. Ideally the keyword approach should be handled using a named
argument syntax. This would be far better than the approach implemented in
this patch. I'd much prefer:
  res = list_dialog(.select="extend", title, list, button1, button2)
or even:
  res = list_dialog(title, list, .select="extend", \
                    .buttons={button1,button2})
than what this patch allows:
  res = list_dialog(title, list, "extend_sel", button1, button2)

I hate that optional keyword!

Although I haven't implemented the named argument version, everything needed
to already exists. What I need is the go-ahead on the syntactic extension
(after the next release).

Tony