git: consolidate mails in commit logs

Map duplicate mails / names in commit logs to a single canonical names.
Useful to report to management with git shortlog -nes

Signed-off-by: Loic Dachary <loic@dachary.org>
Merge pull request #634 from dachary/master

git: consolidate mails in commit logs

Reviewed-by: Sage Weil <sage@inktank.com>