Implement "isOnline" for temporary players.

This corrects the issue seen on http://pastebin.com/C4D8jsja

ProtocolLib/src/main/java/com/comphenix/protocol/injector/server/TemporaryPlayerFactory.java

@@ -102,6 +102,8 @@ public class TemporaryPlayerFactory {
 					throw new IllegalStateException("Unable to find injector.");
 				
 				// Use the socket to get the address
+				if (methodName.equalsIgnoreCase("isOnline"))
+					return injector.getSocket() != null && injector.getSocket().isConnected();
 				if (methodName.equalsIgnoreCase("getName"))
 					return "UNKNOWN[" + injector.getSocket().getRemoteSocketAddress() + "]";
 				if (methodName.equalsIgnoreCase("getPlayer"))