Merge branch 'rj/format-patch-auto-cover-with-interdiff'

"git format-patch --interdiff" for multi-patch series learned to turn on cover letters automatically (unless told never to enable cover letter with "--no-cover-letter" and such). * rj/format-patch-auto-cover-with-interdiff: format-patch: assume --cover-letter for diff in multi-patch series t4014: cleanups in a few tests