[RFC PATCH v2 2/3] emacs: changes to other files to support notmuch-pick

[Mark Walters]

This patch adds 

entries to notmuch-pick to notmuch-hello.el notmuch.el and
notmuch-show.el.

the option to view the current search in pick mode (from either
notmuch-show.el or notmuch.el)

a defcustom group for notmuch-pick.

make notmuch-show (the main function) return the buffer it uses. This is
used by notmuch-pick to try and make sure it only kills the correct
buffer.

Add an extra parameter to notmuch-query-get-threads (in
notmuch-query.el) so that extra parameters can be passed to control the
sort order, the --headers-only option, and threading etc.

Finally add an option to notmuch-show to get it to pass the
--thread=none option (so that just the matching messages are returned
with no threading). This is used to show a single message (e.g. when the
query is a single message-id).

Again advice on how to split up this patch is gratefully received!

Best wishes

Mark