flesh out URL and friends

classpath/java/net/UnknownServiceException.java

@@ -0,0 +1,13 @@
+package java.net;
+
+import java.io.IOException;
+
+public class UnknownServiceException extends IOException {
+  public UnknownServiceException(String message) {
+    super(message);
+  }
+
+  public UnknownServiceException() {
+    this(null);
+  }
+}