.mailmap: update long-lost friends with multiple defunct addresses

.mailmap: update long-lost friends with multiple defunct addresses

A handful of past contributors are recorded with multiple e-mail
addresses, all of which are undeliverable.  With a lot of help from
Jonathan, we located all of them except for one person, and a pair
of addresses we suspect belong to a single person but we are not
certain.

Update the found ones with their currently preferred address, and
use the last known address to consolidate contributions by the lost
one.

Helped-by: Stefan Beller <stefanbeller@googlemail.com>
Helped-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>