Faster/more reliable IP checking

Check if URL can be loaded with cURL, otherwise use file_get_contents. Replaced the existing sites with these 2, as these came up fastest with some simple benchmarks. Alternatives in plain text are:
http://icanhazip.com/
http://phihag.de/ip/
http://ifconfig.me/ip
A reliable with little text is: http://checkip.dyndns.org/ and offcourse the original JSON; http://pv.sohu.com/cityjson?ie=utf-8 (which could be changed to use self::loadUrl() if you want to keep that.

Also added a check to validate the IP, to make sure no html leaks through, when a website changes.