[BUG] git-send-email format-patch awareness & retry

(cc primary authors & Junio)

This is more of a TODO note to myself than a bug, but if someone else
gets around to fixing these that'd be great too.

git-send-email should:

 * Complain loudly on "*** SUBJECT HERE ***" and "*** BLURB HERE ***"

   This should have an additional "are you sure" dialog:

    Subject: [PATCH 00/20] *** SUBJECT HERE ***
    Date: Tue,  7 Sep 2010 16:43:03 +0000
    Message-Id: [ref]
    X-Mailer: git-send-email 1.7.2.3.313.gcd15
    MIME-Version: 1.0
    Content-Type: text/plain; charset=UTF-8
    Content-Transfer-Encoding: 8bit

    Send this email? ([y]es|[n]o|[q]uit|[a]ll): y
    Password:

 * Retry before bailing out:

   It's annoying to lose state because of temporary SMTP errors. This
   should offer to sleep for a few seconds and retry:

    Content-Transfer-Encoding: 8bit

    Send this email? ([y]es|[n]o|[q]uit|[a]ll): y
     Go ahead k83sm4304468weq.14
    4.3.0 Mail server temporarily rejected message. k83sm4304468weq.14

It would also be a lot easier to catch errors in the git-send-email
output if it supported colors, e.g. colored the subject line
differently from others.