Merge branch 'bc/append-signed-off-by'

Consolidate codepaths that inspect log-message-to-be and decide to
add a new Signed-off-by line in various commands.

* bc/append-signed-off-by:
  git-commit: populate the edit buffer with 2 blank lines before s-o-b
  Unify appending signoff in format-patch, commit and sequencer
  format-patch: update append_signoff prototype
  t4014: more tests about appending s-o-b lines
  sequencer.c: teach append_signoff to avoid adding a duplicate newline
  sequencer.c: teach append_signoff how to detect duplicate s-o-b
  sequencer.c: always separate "(cherry picked from" from commit body
  sequencer.c: require a conforming footer to be preceded by a blank line
  sequencer.c: recognize "(cherry picked from ..." as part of s-o-b footer
  t/t3511: add some tests of 'cherry-pick -s' functionality
  t/test-lib-functions.sh: allow to specify the tag name to test_commit
  commit, cherry-pick -s: remove broken support for multiline rfc2822 fields
  sequencer.c: rework search for start of footer to improve clarity

revision.h

@@ -138,7 +138,7 @@ struct rev_info {
 	int		reroll_count;
 	char		*message_id;
 	struct string_list *ref_message_ids;
-	const char	*add_signoff;
+	int		add_signoff;
 	const char	*extra_headers;
 	const char	*log_reencode;
 	const char	*subject_prefix;