[PATCH v3] emacs: support "notmuch new" as a notmuch-poll-script

[Austin Clements]

LGTM.

Quoth Jani Nikula on Dec 12 at 10:50 pm:
> Support nil value for notmuch-poll-script to run "notmuch new" instead of
> an external script, and make this the new default. "notmuch new" is run
> using the configured notmuch-command.
> 
> This allows taking better advantage of the "notmuch new" hooks from emacs
> without intermediate scripts.
> 
> Signed-off-by: Jani Nikula <jani at nikula.org>
> 
> ---
> 
> v3: only documentation changes suggested by Austin and Dmitry.