[Outreachy][PATCH v2 00/11] Finish converting git bisect to C part 1

These patches correspond to a first part of patch series of Outreachy project "Finish converting `git bisect` from shell to C" started by the interns Pranit Bauva and Tanushree Tumane (https://public-inbox.org/git/pull.117.git.gitgitgadget@gmail.com) and continued by Miriam Rubio.

This first part are formed of preparatory/clean-up patches and all `bisect.c` libification work.

These patch series emails were generated from: https://gitlab.com/mirucam/git/commits/git-bisect-work-part1

It has to be noted that in this version 2 nothing has been done about a reviewer suggestion of using enums for error codes, because there was no consensus about using them by the reviewers.

--- Changes since v1 Finish converting git bisect to C part 1 patch series ---

General changes ---------------

* Previous patch series version has been split in smaller groups 
in order to facilitate revision and integration.
* Rebase on master branch: c7a6207591 (Sync with maint, 2020-01-27).
* Improve commit messages.

Specific changes ----------------

[6/11] bisect: libify `exit_if_skipped_commits` to `error_if_skipped*` 
and its dependents
    
* Remove redundant sentences in commit message.
* Use `if (res < 0)` instead of `if (res)`.

[8/11] bisect: libify `check_merge_bases` and its dependents

* Remove redundant sentence in commit message.

--

[9/11] bisect: libify `check_good_are_ancestors_of_bad` and its dependents

* Remove redundant sentences in commit message.
* Return in `if (!current_bad_oid)` condition.

--

[10/11] bisect: libify `handle_bad_merge_base` and its dependents

* Remove redundant sentence in commit message.

--

[11/11] bisect: libify `bisect_next_all`

* Remove redundant sentence in commit message.
* Add return codes explanations in `bisect.h`.

--

Miriam Rubio (2):
  bisect--helper: convert `vocab_*` char pointers to char arrays
  bisect: use the standard 'if (!var)' way to check for 0

Pranit Bauva (7):
  run-command: make `exists_in_PATH()` non-static
  bisect: libify `exit_if_skipped_commits` to `error_if_skipped*` and
    its dependents
  bisect: libify `bisect_checkout`
  bisect: libify `check_merge_bases` and its dependents
  bisect: libify `check_good_are_ancestors_of_bad` and its dependents
  bisect: libify `handle_bad_merge_base` and its dependents
  bisect: libify `bisect_next_all`

Tanushree Tumane (2):
  bisect--helper: change `retval` to `res`
  bisect--helper: introduce new `decide_next()` function

 bisect.c                 | 136 +++++++++++++++++++++++++++------------
 bisect.h                 |  23 +++++++
 builtin/bisect--helper.c | 118 +++++++++++++++++----------------
 run-command.c            |   2 +-
 run-command.h            |  11 ++++
 5 files changed, 193 insertions(+), 97 deletions(-)