Merge branch 'es/format-patch-interdiff' into es/format-patch-rangediff

Merge branch 'es/format-patch-interdiff' into es/format-patch-rangediff

* es/format-patch-interdiff:
  format-patch: allow --interdiff to apply to a lone-patch
  log-tree: show_log: make commentary block delimiting reusable
  interdiff: teach show_interdiff() to indent interdiff
  format-patch: teach --interdiff to respect -v/--reroll-count
  format-patch: add --interdiff option to embed diff in cover letter
  format-patch: allow additional generated content in make_cover_letter()