Merge branch 'jc/signed-commit' and 'jc/pull-signed-tag'

They both use the extended headers in commit objects, and the former has
necessary infrastructure to show them that is useful to view the result of
the latter.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --cc builtin/commit.c
index 0c64c880d5fe7106e391e677f6a32dd46e73b36b,7e8a1cf4e074053a78f2f029e8c03f17c9053bf0..fa41ec8c878a6af63e17b79996148be85dcfccef
--- 1/builtin/commit.c
--- 2/builtin/commit.c
+++ b/builtin/commit.c
@@@ -1484,15 -1493,11 +1493,15 @@@ int cmd_commit(int argc, const char **a
                exit(1);
        }
  
 -      if (amend)
 +      if (amend) {
                extra = read_commit_extra_headers(current_head);
 +      } else {
 +              struct commit_extra_header **tail = &extra;
 +              append_merge_tag_headers(parents, &tail);
 +      }
  
        if (commit_tree_extended(sb.buf, active_cache_tree->sha1, parents, sha1,
-                                author_ident.buf, extra)) {
+                                author_ident.buf, sign_commit, extra)) {
                rollback_index_files();
                die(_("failed to write commit object"));
        }