Add DynDNS No-IP Free account support 

The free No-IP account requires the IP address to be changed within every 30 days. If there is no change, the "last updated" date at No-IP does not get updated and the account lapses.
This change implements a double-update when the cache age reaches 25 days, or the user does "Save & Force Update" on the GUI. It updates the IP to a dummy address (192.168.1.1) and then 10 seconds later puts it back the way it was. After this process, the "last updated" date on the No-IP site updates.
To get this behaviour, users have to select "No-IP (free)" as their DynDNS service type. Existing "No-IP" users will not have this behaviour (for the No-IP paid accounts it is not necessary). For other DynDNS providers, the code logic is unchanged.
Forum: http://forum.pfsense.org/index.php/topic,59231.0.html