Better public .connected property

[rauchg]

Right now .connected doesn't indicate if the connection is considered disconnected, but rather if there's an open request for a client. If the client is in a a long-polling disconnection, .connected will be false even though the "socket" is still considered connected.

finalized should be removed, connected should be named open or similar (or maybe use a readyState property with number codes), and an actual connected with the expected behavior should be introduced.

[rauchg]

.connected renamed to ._open, and adopted proper connected (closed by d041572)
example/client updated to latest socket.io client