[GSoC][PATCH v2 0/7] rebase -i: rewrite some parts in C

This patch series rewrites some parts of interactive rebase from shell to C:

 - append_todo_help(). The C version covers a bit more than the shell
   version.

 - The edit-todo functionnality.

 - The reflog operations.

The v1 of this series is an aggregate made by Junio of my patch series about append_todo_help() (v3), edit-todo (v2) and reflog (v5), and can be found in the branch `ag/rebase-i-in-c`.

This branch is based on master (as of 2018-07-02).

Changes since v1:

 - Introducing rebase-interactive.c to contain functions necessary for
   interactive rebase.

 - Show an error message when append_todo_help() fails to edit the todo
   list.

 - Renaming enumeration check_level and its values to avoid namespace
   pollution.

 - Moving append_todo_help() and edit_todo() from sequencer.c to
   interactive-rebase.c.

Alban Gruin (7):
  sequencer: make two functions and an enum from sequencer.c public
  rebase--interactive: rewrite append_todo_help() in C
  editor: add a function to launch the sequence editor
  rebase-interactive: rewrite the edit-todo functionality in C
  sequencer: add a new function to silence a command, except if it
    fails.
  rebase -i: rewrite setup_reflog_action() in C
  rebase -i: rewrite checkout_onto() in C

 Makefile                   |   1 +
 builtin/rebase--helper.c   |  24 +++++++-
 cache.h                    |   1 +
 editor.c                   |  27 ++++++++-
 git-rebase--interactive.sh | 100 +++----------------------------
 rebase-interactive.c       |  99 ++++++++++++++++++++++++++++++
 rebase-interactive.h       |   7 +++
 sequencer.c                | 120 +++++++++++++++++++++++++------------
 sequencer.h                |  14 +++++
 strbuf.h                   |   2 +
 10 files changed, 260 insertions(+), 135 deletions(-)
 create mode 100644 rebase-interactive.c
 create mode 100644 rebase-interactive.h