Bug 158065 [DataBinding] ValidationError observables need a nudge to hook themselves up
See attached patch.
bundles/org.eclipse.jface.databinding/src/org/eclipse/jface/databinding/observable/value/ComputedValue.java
IStaleListener {
		public void run() {
			cachedValue = calculate();
		}
		public void handleStale(IObservable source) {
			if (!dirty && !stale) {
				stale = true;
				fireStale();
			}
		}
		public void handleChange(IObservable source) {
			makeDirty();
		}
	}
	private PrivateInterface privateInterface = new PrivateInterface();
	private Object valueType;
	public final Object doGetValue() {
		if (dirty) {