Better mechanism to choose the default editor (and avoid vi if possible)?

[Marcin Kasperski]

>
> You need an editor to set the editor, so a default is required.
>

Whenever I commit without having ui.username, I get:

  $ hg commit -m Hello
  abort: no username supplied
  (use 'hg config --edit' to set your username)

IIRC second line wasn't always there and we managed to live
(of course hg config --edit is improvement).

Still I don't think it would be horrible to face

  $ hg something
  abort: editor is not configured
  (see `hg help setting-editor` or http://some/page/with/info
   to find out how to configure your editor)

Surely for some it would be better than land in vi, and for everybody
it is better than land in non-existing vi. 

And help-page can give exact examples for popular choices