[PATCH v2 0/2] Avoid forking a process when checking merge bases

The goal of this patch series is to check if good revisions are
ancestor of the bad revision without forking a process to launch
"git rev-list $good ^$bad".

This new version of this patch series does not use an "unparse_commit"
function anymore, we use "clear_commit_marks" instead.

  bisect: rework some rev related functions to make them more reusable
  bisect: check ancestors without forking a "git rev-list" process

 bisect.c                    |   79 +++++++++++++++++++-----------------------
 t/t6030-bisect-porcelain.sh |   13 +------
 2 files changed, 37 insertions(+), 55 deletions(-)