InetAddress.java (toString): Use hostname when not null, don't do an explicit reverse getHostName() lookup.

* java/net/InetAddress.java (toString): Use hostname when not null,
        don't do an explicit reverse getHostName() lookup.
        * java/net/Socket.java (setSocketImplFactory): When fac == null throw
        NullPointerException.

From-SVN: r59902

libjava/java/net/Socket.java

@@ -892,6 +892,9 @@ public class Socket
     if (sm != null)
       sm.checkSetFactory();
 
+    if (fac == null)
+      throw new SocketException("SocketImplFactory cannot be null");
+
     factory = fac;
   }