Bug 65276 [Preferences] Preference dialog should disable OK when okPressed
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferenceDialog.java
cancelPressed();
				return;
			}
			case IDialogConstants.HELP_ID : {
				helpPressed();
				return;
			}
		}
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.jface.dialogs.Dialog#cancelPressed()
	 */
	protected void cancelPressed() {
		
		Iterator nodes = preferenceManager.getElements(
				PreferenceManager.PRE_ORDER).iterator();
		while (nodes.hasNext()) {
			final IPreferenceNode node = (IPreferenceNode) nodes.next();
			if (node.getPage() != null) {
				Platform.run(new SafeRunnable() {
					public void run() {
						if (!node.getPage().performCancel())
							return;
					}
				});
			}
		}
		setReturnCode(CANCEL);