patch, 5 partsCover letter for format-patch series

This should take care of all of the comments, so far as they're practical to do in the initial series. Future work will include making the cover letter include useful shortlog and diffstat (if possible) for arguments that aren't a single linear and bounded series (at present, doing anything too tricky results in a cover letter without shortlog or diffstat).

Also, I haven't done anything here about making format-patch give an error if the series is empty, whether or not --cover-letter is used.

Note that [1/5] is new tests for format-patch, and independant of this series except in so far as it demonstrates that I haven't broken these things.

Daniel Barkalow (5):
      Add more tests for format-patch
      Improve message-id generation flow control for format-patch
      Export some email and pretty-printing functions
      Retain extra blank lines between the summary and the body
      Add a --cover-letter option to format-patch

 Documentation/git-format-patch.txt                 |   20 +-
 builtin-log.c                                      |  261 ++++++++++++++------
 commit.h                                           |   15 ++
 log-tree.c                                         |  126 +++++-----
 log-tree.h                                         |    2 +
 pretty.c                                           |   38 ++--
 revision.h                                         |    2 +-
 t/t4013-diff-various.sh                            |    1 +
 ...tch_--stdout_--cover-letter_-n_initial..master^ |  101 ++++++++
 t/t4014-format-patch.sh                            |   71 ++++++
 10 files changed, 477 insertions(+), 160 deletions(-)
 create mode 100644 t/t4013/diff.format-patch_--stdout_--cover-letter_-n_initial..master^