Bug 65276 [Preferences] Preference dialog should disable OK when okPressed
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferenceDialog.java
/**
	 * The minimum page size; 400 by 400 by default.
	 * 
	 * @see #setMinimumPageSize(Point)
	 */
	private Point minimumPageSize = new Point(400, 400);
	/**
	 * The OK button.
	 */
	private Button okButton;
	/**
	 * The Composite in which a page is shown.
	 */
	private Composite pageContainer;
	/**
	 * The preference manager.
	 */
	private PreferenceManager preferenceManager;
	/**
	 * Flag for the presence of the error message.
	 */
	private boolean showingError = false;
	/**
	 * Preference store, initially <code>null</code> meaning none.
	 * 
	 * @see #setPreferenceStore
	 */
	private IPreferenceStore preferenceStore;
	private Composite titleArea;
	private Label titleImage;