[MERGE] Add mail-mode GNU Emacs mail package as a mail_client option.

[Ian Clatworthy]

Xavier Maillard wrote:
> Hi,
> 
>> I'll make these tweaks and merge.
> 
> Please do not merge this patch. I have sent a new patch taking into account all
> Aaron's comments. Sadly, some of yours won't be addressed but I will be able to
> tackle them soon.

It's just finished merging sorry - rev 3323 in bzr.dev. Is there harm in
leaving the code in bzr.dev? If so, I can always commit a new version
that backs out the change. Assuming the current code is a step forward,
it may be best to leave it there until your follow-up patch supercedes it?

Either way, if you merge from bzr.dev now, you'll get my tweaks included
in your follow-up patch.

Ian C.