[PATCH v2 0/4] Add an option to git-format-patch to record base tree info

This is a re-roll of 

   http://article.gmane.org/gmane.comp.version-control.git/286873

It is almost a rewrite of v1, Changes include:

 - Make commit_patch_id() a publib helper function, so it can be available to other modules.

 - The new option "--base" will not only record the base commit id(a public well-known commit),
   but also the prerequisite patches's patch ids, then the 0day test robot could get these info,
   thus to checkout the well-known base tree-ish, apply the prerequisite patches and then the
   patches being send can be applied to correct tree to be evaluated. (0day catches every patch
   series to LKML and maintains a patch-id => commit-id database for in-flight patches.)

 - For developers' convenience, we propose a new format.base configuration to track the base commit
   automatically, if current branch the developer work on has its remote-tracking branch,
   the base commit would be the tip commit of the remote branch, if current branch is not tracked
   with any remote branch(eg. checkout by a local branch or a commit), thus its upstream could not
   be obtained, it will just record the parent commit-id of the patch series, as well as patch-id for
   reference.

   so here is the text UI:

   1) for the cases that exact base commit could be obtained(eithor from manual input --base=<base-commit-id>
	   or from upstream if base=auto is set) 

	 ** base-commit-info **
	 base-commit: ab5d01a29eb7380ceab070f0807c2939849c44bc
	 prerequisite-patch-id: 61400f965fdc0c2fbe8ad9cb5316c3efe6e05c14
	 prerequisite-patch-id: 063a398ef398647d8d839e6f9090d38ea9e0551c

   2) for cases that exact base commit is failed to obtained
	
	 ** parent-commit-info **
	 parent-commit: ab5d01a29eb7380ceab070f0807c2939849c44bc
	 parent-patch-id: caf2dae24db5b4c49a6c4134dd6d9908e898424b

Thanks for fengguang and junio's suggestions and prototype of implementation.

Thanks, Xiaolong.

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 |  20 ++++++
 builtin/log.c                      | 137 +++++++++++++++++++++++++++++++++++++
 patch-ids.c                        |   2 +-
 patch-ids.h                        |   2 +
 4 files changed, 160 insertions(+), 1 deletion(-)