Merge branch 'maint'

Merge branch 'maint'

* maint:
  tutorial: gentler illustration of Alice/Bob workflow using gitk
  pretty=format: respect date format options
  make git-shell paranoid about closed stdin/stdout/stderr
  Document gitk --argscmd flag.
  Fix '--dirstat' with cross-directory renaming
  for-each-ref: Allow a trailing slash in the patterns