[PATCH/RFC] add --authorship-order flag to git log / rev-list

This is my first time submitting a patch to this list, so please, let me know if I'm doing any of this the wrong way! I've striven to follow `Documentation/SubmittingPatches`. I hope I've succeeded. For that matter, it's my first time diving into git's sources, so I obviously would love some commentary on the patch itself, as well. ;)

I've tried herein to add an `--authorship-order` flag to complement git-log's `--topo-order` and `--date-order` flags; it should operate the same as `--date-order`, but using the `AUTHOR_DATE` instead of the `COMMITTER_DATE`.

I've sent an e-mail to this list, previously, on this subject; I'd make this patchset a reply to that, except I have no idea what the in-reply-to should be: http://www.spinics.net/lists/git/msg208542.html

The original work is all on GitHub: https://github.com/git/git/pull/40 https://github.com/ELLIOTTCABLE/git/compare/master...author-order+

elliottcable (1):
  rev-list: add --authorship-order alternative ordering

 builtin/log.c                          |  2 +-
 builtin/rev-list.c                     |  1 +
 builtin/rev-parse.c                    |  1 +
 builtin/show-branch.c                  | 12 ++++-
 commit.c                               | 83 ++++++++++++++++++++++++++++++----
 commit.h                               |  3 +-
 contrib/completion/git-completion.bash |  4 +-
 po/de.po                               |  4 +-
 po/git.pot                             |  2 +-
 po/sv.po                               |  4 +-
 po/vi.po                               |  4 +-
 po/zh_CN.po                            |  4 +-
 revision.c                             | 11 ++++-
 revision.h                             |  1 +
 14 files changed, 110 insertions(+), 26 deletions(-)