pretty: prepare notes message at a centralized place

Instead of passing a boolean show_notes around, pass an optional
string that is to be inserted after the log message proper is shown.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/log-tree.c b/log-tree.c
index c894930..84e9f5b 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -540,7 +540,6 @@
 	struct pretty_print_context ctx = {0};
 
 	opt->loginfo = NULL;
-	ctx.show_notes = opt->show_notes;
 	if (!opt->verbose_header) {
 		graph_show_commit(opt->graph);
 
@@ -648,6 +647,18 @@
 	if (!commit->buffer)
 		return;
 
+	if (opt->show_notes) {
+		int raw;
+		struct strbuf notebuf = STRBUF_INIT;
+
+		raw = (opt->commit_format == CMIT_FMT_USERFORMAT);
+		format_display_notes(commit->object.sha1, &notebuf,
+				     get_log_output_encoding(), raw);
+		ctx.notes_message = notebuf.len
+			? strbuf_detach(&notebuf, NULL)
+			: xcalloc(1, 1);
+	}
+
 	/*
 	 * And then the pretty-printed message itself
 	 */
@@ -689,6 +700,7 @@
 	}
 
 	strbuf_release(&msgbuf);
+	free(ctx.notes_message);
 }
 
 int log_tree_diff_flush(struct rev_info *opt)