Merge branch 'js/am-3-merge-recursive-direct'

"git am -3" calls "git merge-recursive" when it needs to fall back
to a three-way merge; this call has been turned into an internal
subroutine call instead of spawning a separate subprocess.

* js/am-3-merge-recursive-direct:
  merge-recursive: flush output buffer even when erroring out
  merge_trees(): ensure that the callers release output buffer
  merge-recursive: offer an option to retain the output in 'obuf'
  merge-recursive: write the commit title in one go
  merge-recursive: flush output buffer before printing error messages
  am -3: use merge_recursive() directly again
  merge-recursive: switch to returning errors instead of dying
  merge-recursive: handle return values indicating errors
  merge-recursive: allow write_tree_from_memory() to error out
  merge-recursive: avoid returning a wholesale struct
  merge_recursive: abort properly upon errors
  prepare the builtins for a libified merge_recursive()
  merge-recursive: clarify code in was_tracked()
  die(_("BUG")): avoid translating bug messages
  die("bug"): report bugs consistently
  t5520: verify that `pull --rebase` shows the helpful advice when failing

sequencer.c

@@ -293,6 +293,9 @@ static int do_recursive_merge(struct commit *base, struct commit *next,
 	clean = merge_trees(&o,
 			    head_tree,
 			    next_tree, base_tree, &result);
+	strbuf_release(&o.obuf);
+	if (clean < 0)
+		return clean;
 
 	if (active_cache_changed &&
 	    write_locked_index(&the_index, &index_lock, COMMIT_LOCK))
@@ -559,6 +562,8 @@ static int do_pick_commit(struct commit *commit, struct replay_opts *opts)
 	if (!opts->strategy || !strcmp(opts->strategy, "recursive") || opts->action == REPLAY_REVERT) {
 		res = do_recursive_merge(base, next, base_label, next_label,
 					 head, &msgbuf, opts);
+		if (res < 0)
+			return res;
 		write_message(&msgbuf, git_path_merge_msg());
 	} else {
 		struct commit_list *common = NULL;