Bug 65276 [Preferences] Preference dialog should disable OK when okPressed
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferenceDialog.java
/**
	 * The tree viewer.
	 */
	private TreeViewer treeViewer;
	/**
	 * Creates a new preference dialog under the control of the given preference
	 * manager.
	 * 
	 * @param parentShell
	 *            the parent shell
	 * @param manager
	 *            the preference manager
	 */
	public PreferenceDialog(Shell parentShell, PreferenceManager manager) {
		super(parentShell);
		setShellStyle(getShellStyle() | SWT.RESIZE | SWT.MAX);
		preferenceManager = manager;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.jface.dialogs.Dialog#buttonPressed(int)
	 */
	protected void buttonPressed(int buttonId) {
		switch (buttonId) {
			case IDialogConstants.OK_ID : {
				okPressed();
				return;
			}
			case IDialogConstants.CANCEL_ID : {