This adds "creator" (which is parallel to "tagger" or "committer")
and "creatordate" (corresponds to "taggerdate" and
"committerdate").
As other "date" fields, "creatordate" sorts numerically
and displays human readably. This allows for example for
sorting together heavyweigth and lightweight tags.
Signed-off-by: Junio C Hamano <junkio@cox.net> Acked-by: Jakub Narebski <jnareb@gmail.com>