Merge branch 'pn/commit-autosquash'

Merge branch 'pn/commit-autosquash'

* pn/commit-autosquash:
  add tests of commit --squash
  commit: --squash option for use with rebase --autosquash
  add tests of commit --fixup
  commit: --fixup option for use with rebase --autosquash
  pretty.c: teach format_commit_message() to reencode the output
  commit: helper methods to reduce redundant blocks of code

Conflicts:
	Documentation/git-commit.txt
	t/t3415-rebase-autosquash.sh