Merge branch 'ab/submodule-cleanup' into gc/submodule-use-super-prefix

Merge branch 'ab/submodule-cleanup' into gc/submodule-use-super-prefix

* ab/submodule-cleanup:
  git-sh-setup.sh: remove "say" function, change last users
  git-submodule.sh: use "$quiet", not "$GIT_QUIET"
  submodule--helper: eliminate internal "--update" option
  submodule--helper: understand --checkout, --merge and --rebase synonyms
  submodule--helper: report "submodule" as our name in some "-h" output
  submodule--helper: rename "absorb-git-dirs" to "absorbgitdirs"
  submodule update: remove "-v" option
  submodule--helper: have --require-init imply --init
  git-submodule.sh: remove unused top-level "--branch" argument
  git-submodule.sh: make the "$cached" variable a boolean
  git-submodule.sh: remove unused $prefix variable
  git-submodule.sh: remove unused sanitize_submodule_env()