Merge branch 'jk/for-each-ref'

Merge branch 'jk/for-each-ref'

* jk/for-each-ref:
  for-each-ref: add split message parts to %(contents:*).
  for-each-ref: handle multiline subjects like --pretty
  for-each-ref: refactor subject and body placeholder parsing
  t6300: add more body-parsing tests
  t7004: factor out gpg setup