Merge branch 'nd/format-patch-stat-width'

"git format-patch" learned to give 72-cols to diffstat, which is
consistent with other line length limits the subcommand uses for
its output meant for e-mails.

* nd/format-patch-stat-width:
  format-patch: reduce patch diffstat width to 72
  format-patch: keep cover-letter diffstat wrapped in 72 columns