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
* set the margins of this <code>Layout</code> to 0 pixels. 
	 * </p>
	 *
	 * @param parent the parent composite
	 * @return the new control
	 */
	protected abstract Control createContents(Composite parent);
	/**
	 * The <code>PreferencePage</code> implementation of this 
	 * <code>IDialogPage</code> method creates a description label
	 * and button bar for the page. It calls <code>createContents</code>
	 * to create the custom contents of the page.
	 * <p>
	 * If a subclass that overrides this method creates a <code>Composite</code>
	 * that has a layout with default margins (for example, a <code>GridLayout</code>)
	 * it is expected to set the margins of this <code>Layout</code> to 0 pixels.
	 */
	public void createControl(Composite parent) {
		GridData gd;
		Composite content = new Composite(parent, SWT.NULL);
		setControl(content);
		GridLayout layout = new GridLayout();
		layout.marginWidth = 0;
		layout.marginHeight = 0;
		content.setLayout(layout);
		
		applyDialogFont(content);
		
		initializeDialogUnits(content);
		descriptionLabel = createDescriptionLabel(content);