add a bunch of classes to classpath and flesh out a few existing ones

classpath/java/lang/ClassNotFoundException.java

@@ -0,0 +1,15 @@
+package java.lang;
+
+public class ClassNotFoundException extends Exception {
+  public ClassNotFoundException(String message, Throwable cause) {
+    super(message, cause);
+  }
+
+  public ClassNotFoundException(String message) {
+    this(message, null);
+  }
+
+  public ClassNotFoundException() {
+    this(null, null);
+  }
+}