Socket::address: add isAny, setAny, isLoopback, setLoopback, any, loopback

These methods allow to check for a loopback or any address, or set these special addresses in a protocol independent way.
Socket::address: add unit tests for new features
Merge pull request #13 from aberaud/socket_any_loopback

Socket::address: add isAny, setAny, isLoopback, setLoopback