Merge branch 'bw/format-patch-o-create-leading-dirs'

"git format-patch -o <outdir>" did an equivalent of "mkdir <outdir>"
not "mkdir -p <outdir>", which is being corrected.

* bw/format-patch-o-create-leading-dirs:
  format-patch: create leading components of output directory

diff --cc builtin/log.c
Simple merge

diff --cc t/t4014-format-patch.sh
Simple merge