Bug 41927 [Dialogs] Selecting in PreferenceDialog generates too many invalid entries
20030825 If you select an entry, close the dialog and then reopen it selecting anotehr entry will result in a "this page has invalid values" although you selected nothing.
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferencePage.java
/**
	 * Performs special processing when this page's Apply button has been pressed.
	 * <p>
	 * This is a framework hook method for sublcasses to do special things when
	 * the Apply button has been pressed.
	 * The default implementation of this framework method simply calls
	 * <code>performOk</code> to simulate the pressing of the page's OK button.
	 * </p>
	 * 
	 * @see #performOk
	 */
	protected void performApply() {
		performOk();
	}
	/**	
	 * The preference page implementation of an <code>IPreferencePage</code>
	 * method performs special processing when this page's Cancel button has
	 * been pressed.
	 * <p>
	 * This is a framework hook method for sublcasses to do special things when
	 * the Cancel button has been pressed. The default implementation of this
	 * framework method does nothing and returns <code>true</code>.
	 */
	public boolean performCancel() {
		return true;
	}
	/**
	 * Performs special processing when this page's Defaults button has been pressed.
	 * <p>
	 * This is a framework hook method for sublcasses to do special things when