MRBS 1.12.2 等保2.0二级整改完整提交

包含：登录失败锁定、90天密码有效期、30分钟会话超时、
强制改密、登录审计日志、屏幕水印、企业背景图、
备案信息固定底部、favicon、JS空集合保护、
会话过期体验优化（403 JSON）、display_errors 关闭、
固定 key 根治 Integrity check failed 等全部改动

注意：config.inc.php/.htaccess/.user.ini 含敏感信息，
通过 .gitignore 排除，勿推送到公开仓库。

upgrade/51/mysql.sql

@@ -0,0 +1 @@
+#

upgrade/51/post.inc

@@ -0,0 +1,14 @@
+<?php
+namespace MRBS;
+
+// Make sure that any null values for the periods column are replaced with
+// the config default.  (It's possible that somebody working from the latest
+// default branch could have created a new area with a null value.  That has
+// now been fixed, so won't happen again, but we need to clean up the area
+// table just in case).
+
+global $periods;
+
+$sql = "UPDATE " . _tbl('area') . " SET periods = ? WHERE periods IS NULL";
+
+$upgrade_handle->command($sql, array(json_encode($periods)));