[PATCH/WIP v2 00/19] Make git-am a builtin

This is a re-roll of [v1]. Thanks Junio, Torsten, Jeff, Eric for the reviews last round.

Previous versions:

[v1] http://thread.gmane.org/gmane.comp.version-control.git/270048

git-am is a commonly used command for applying a series of patches from a mailbox to the current branch. Currently, it is implemented by the shell script git-am.sh. However, compared to C, shell scripts have certain deficiencies: they need to spawn a lot of processes, introduce a lot of dependencies and cannot take advantage of git's internal caches.

This WIP patch series rewrites git-am.sh into optimized C builtin/am.c, and is part of my GSoC project to rewrite git-pull and git-am into C builtins[1].

[1] https://gist.github.com/pyokagan/1b7b0d1f4dab6ba3cef1

Paul Tan (19):
  wrapper: implement xopen()
  wrapper: implement xfopen()
  am: implement skeletal builtin am
  am: implement patch queue mechanism
  am: split out mbox/maildir patches with git-mailsplit
  am: detect mbox patches
  am: extract patch, message and authorship with git-mailinfo
  am: apply patch with git-apply
  am: commit applied patch
  am: refresh the index at start
  am: refuse to apply patches if index is dirty
  am: implement --resolved/--continue
  am: implement --skip
  am: implement --abort
  am: implement quiet option
  am: exit with user friendly message on patch failure
  am: implement am --signoff
  cache-tree: introduce write_index_as_tree()
  am: implement 3-way merge

 Makefile          |    1 +
 builtin.h         |    1 +
 builtin/am.c      | 1214 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 cache-tree.c      |   29 +-
 cache-tree.h      |    1 +
 git-compat-util.h |    2 +
 git.c             |    1 +
 wrapper.c         |   43 ++
 8 files changed, 1280 insertions(+), 12 deletions(-)
 create mode 100644 builtin/am.c