implement primitive heap dump facility for memory profiling, accessible via Runtime.dumpHeap

The proper way to do this is to implement a subset of JVMTI, but this
will do the job for now.

classpath/java/lang/reflect/Method.java

@@ -111,8 +111,8 @@ public class Method<T> extends AccessibleObject implements Member {
     }
   }
 
-  public static native Object invoke(Method method, Object instance,
-                                     Object ... arguments)
+  private static native Object invoke(Method method, Object instance,
+                                      Object ... arguments)
     throws InvocationTargetException, IllegalAccessException;
 
   public Class getReturnType() {