rerere: error out on autoupdate failure

We have been silently tolerating errors by returning early with an
error that the caller ignores since rerere.autoupdate was introduced
in v1.6.0-rc0~120^2 (2008-06-22).  So on error (for example if the
index is already locked), rerere can return success silently without
updating the index or with only some items in the index updated.

Better to treat such failures as a fatal error so the operator can
figure out what is wrong and fix it.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

rerere.c

@@ -476,27 +476,23 @@ out:
 
 static struct lock_file index_lock;
 
-static int update_paths(struct string_list *update)
+static void update_paths(struct string_list *update)
 {
 	int i;
-	int fd = hold_locked_index(&index_lock, 0);
-	int status = 0;
 
-	if (fd < 0)
-		return -1;
+	hold_locked_index(&index_lock, 1);
 
 	for (i = 0; i < update->nr; i++) {
 		struct string_list_item *item = &update->items[i];
-		if (add_file_to_cache(item->string, ADD_CACHE_IGNORE_ERRORS))
-			status = -1;
+		if (add_file_to_cache(item->string, 0))
+			exit(128);
 	}
 
-	if (!status && active_cache_changed) {
+	if (active_cache_changed) {
 		if (write_locked_index(&the_index, &index_lock, COMMIT_LOCK))
 			die("Unable to write new index file");
-	} else if (fd >= 0)
+	} else
 		rollback_lock_file(&index_lock);
-	return status;
 }
 
 static int do_plain_rerere(struct string_list *rr, int fd)