RFC/PATCH emacs attachment handling

[Mark Walters]

>> To user that is:
>>
>> Pressing Enter on top of an attachment will either show the attachment on
>> buffer (in case there is 'converter' defined) or offer to save the
>> attachment. Pressing 'o' on top of an attachment will always offer to save
>> the attachment.
>
> I really do not like it this behaviour. I'd rather want easy to memorize
> keybindings: 'v'iew,'s'ave, etc.

I am happy either way. I think a bigger question is about what re-use
of keys is sensible between the normal notmuch-show map (when not over
the button) and this new button map. For example using `a' in the
button map seems like it would cause accidental archiving of threads
(when you happen not be over the button).

Perhaps using v and w so v means view and w means save: if over the
body it applies to all attachments if over a button just to that
single attachment. (We would still need a new key for the "open-with"
behaviour.)

Best wishes

Mark