Bug 273330 [JFace] Add API to MessageDialog to enable clients to use SWT.SHEET
A new style constant SWT.SHEET was added recently. Without adding new API in JFace, clients who are currently using the convenience methods MessageDialog.openWarning/Error/Information/Question/Confirmation would not be able to open these dialogs as sheets.
bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/MessageDialog.java
* Opens this message dialog, creating it first if it has not yet been created.
	 * <p>
	 * This method waits until the dialog is closed by the end user, and then it
	 * returns the dialog's return code. The dialog's return code is either the
	 * index of the button the user pressed, or {@link SWT#DEFAULT} if the dialog
	 * has been closed by other means.
	 * </p>
	 *
	 * @return the return code
	 *
	 * @see org.eclipse.jface.window.Window#open()
	 */
    public int open() {
    	return super.open();
    }
    /**
     * Convenience method to open a simple confirm (OK/Cancel) dialog.
     * 
     * @param parent
     *            the parent shell of the dialog, or <code>null</code> if none
     * @param title
     *            the dialog's title, or <code>null</code> if none
     * @param message
     *            the message
     * @return <code>true</code> if the user presses the OK button,
     *         <code>false</code> otherwise
     */
    public static boolean openConfirm(Shell parent, String title, String message) {
        MessageDialog dialog = new MessageDialog(parent, title, null,