Merge branch 'kh/format-patch-noprefix-is-boolean' into next

The configuration variable format.noprefix did not behave as a
proper boolean variable, which has now been fixed and documented.

* kh/format-patch-noprefix-is-boolean:
  doc: diff-options.adoc: show format.noprefix for format-patch
  format-patch: make format.noprefix a boolean

diff --cc builtin/log.c
Simple merge

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