blame: move show_root flag to scoreboard

The show_root flag is used in parts of blame that are being moved to
libgit, and should be accessible via the scoreboard structure.

Signed-off-by: Jeff Smith <whydoubt@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/blame.c

@@ -384,6 +384,7 @@ struct blame_scoreboard {
 
 	/* flags */
 	int reverse;
+	int show_root;
 };
 
 static void sanity_check_refcnt(struct blame_scoreboard *);
@@ -1784,7 +1785,7 @@ static void assign_blame(struct blame_scoreboard *sb, int opt)
 				mark_parents_uninteresting(commit);
 		}
 		/* treat root commit as boundary */
-		if (!commit->parents && !show_root)
+		if (!commit->parents && !sb->show_root)
 			commit->object.flags |= UNINTERESTING;
 
 		/* Take responsibility for the remaining entries */
@@ -2885,6 +2886,8 @@ parse_done:
 	if (blame_copy_score)
 		sb.copy_score = blame_copy_score;
 
+	sb.show_root = show_root;
+
 	read_mailmap(&mailmap, NULL);
 
 	assign_blame(&sb, opt);