patch, 5 partsport more "git bisect next" code to C

This patch series moves code from the "bisect_next" shell function in "git-bisect.sh" to C code in "builtin-bisect--helper.c".

To do that a "--next-exit" option to "git bisect--helper" is added, and is used instead of the "--next-vars" option in "bisect_next".

  rev-list: make "estimate_bisect_steps" non static
  rev-list: refactor printing bisect vars
  bisect: move common bisect functionality in "bisect_common"
  bisect--helper: add "--next-exit" to output bisect results
  bisect: use "git bisect--helper --next-exit" in "git-bisect.sh"

 bisect.c                 |  127 +++++++++++++++++++++++++++++++++++++++++++---
 bisect.h                 |    7 +++
 builtin-bisect--helper.c |   12 +++-
 builtin-rev-list.c       |   63 ++++++++++++-----------
 git-bisect.sh            |   39 +++-----------
 5 files changed, 178 insertions(+), 70 deletions(-)