Bug 24157 [Dialogs] MessageDialog needs to setFocus on default button
As the MessageDialog by default has no other widgets to set focus on we need to set focus on the default button to prevent it getting slammed by the default SWT behaviour.
bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/MessageDialog.java
/**
	 * Dialog title (a localized string).
	 */
	private String title;
	/**
	 * Dialog title image.
	 */
	private Image titleImage;
	
	/**
	 * Message (a localized string).
	 */
	private String message;
	/**
	 * Image, or <code>null</code> if none.
	 */
	private Image image = null;
/**
 * Create a message dialog.
 * Note that the dialog will have no visual representation (no widgets)
 * until it is told to open.
 * <p>
 * The labels of the buttons to appear in the button bar are supplied in this
 * constructor as an array. The <code>open</code> method will return the index
 * of the label in this array corresponding to the button that was pressed to 
 * close the dialog. If the dialog was dismissed without pressing a button (ESC, etc.)
 * then -1 is returned. Note that the <code>open</code> method blocks.
 * </p>
 *
 * @param parentShell the parent shell