v2.4.5-6pre

Update ShadowsocksR source code to latest trunk (23/Apr SHA: a8c4b5c).
Watchdog script now support auto-switch between main and backup server.
Fixed some bugs.

Padavan firmware install scripts:
wget -q http://dwz.cn/ssr-padavan-6 -O - | tar -xjvf - -C /etc && mtd_storage.sh save
nvram set crond_enable=1 && nvram commit