[PATCH v4 0/4] Add --base option to git-format-patch to record base tree info

V4 mainly addresses Junio's comments on V3, Changes include:

 - Polish up the documentation to make output files git-format-patch.1 and
   git-format-patch.html more sensible.

 - Add error handling when base commit is not ancestor of revision list
   specified in cmdline.

 - Specify topo order to do the traverse work, and show the base tree info
   block in a more natural sequence.
 
 - If --base=auto is set and there is more than one best merge base, instead
   of picking up a random one, it will error out for they may be complicated
   situation such as criss-cross merges.

 - Add tests for the --base option and format.base configuration.

 - Fix a segfault error due to bases structure hasn't been initialized when
   --base option is not set, Thanks for Ramsay's report.

Xiaolong Ye (4):
  patch-ids: make commit_patch_id() a public helper function
  format-patch: add '--base' option to record base tree info
  format-patch: introduce --base=auto option
  format-patch: introduce format.base configuration

 Documentation/git-format-patch.txt |  64 +++++++++++++++++++
 builtin/log.c                      | 123 +++++++++++++++++++++++++++++++++++++
 patch-ids.c                        |   2 +-
 patch-ids.h                        |   2 +
 t/t4014-format-patch.sh            |  48 +++++++++++++++
 5 files changed, 238 insertions(+), 1 deletion(-)