Merge branch 'ac/usage-string-fixups'

Usage-string normalization.

* ac/usage-string-fixups:
  amend remaining usage strings according to style guide

diff --cc builtin/bisect--helper.c
Simple merge

diff --cc builtin/reflog.c
Simple merge

diff --cc builtin/submodule--helper.c
Simple merge

diff --cc diff.c
Simple merge