Merge branch 'pw/3.0-commentchar-auto-deprecation' into next

Proposes to deprecate "core.commentChar=auto" that attempts to
dynamically pick a suitable comment character, as it is too much
trouble to support for little benefit.

* pw/3.0-commentchar-auto-deprecation:
  commit: print advice when core.commentString=auto
  config: warn on core.commentString=auto
  breaking-changes: deprecate support for core.commentString=auto

diff --cc Documentation/config/core.adoc
Simple merge

diff --cc builtin/commit.c
Simple merge

diff --cc builtin/merge.c
Simple merge

diff --cc builtin/rebase.c
Simple merge

diff --cc builtin/revert.c
Simple merge

diff --cc config.c
Simple merge

diff --cc environment.c
Simple merge

diff --cc repository.c
Simple merge

diff --cc t/t3404-rebase-interactive.sh
Simple merge