.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 undeliberable.  With a lot of help from
Jonathan, we located all of them except for one.  Update the found
ones with their currently preferred address, and use the last known
address to consolidate contributions by the lost person under a
single entry.

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