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/MessageDialogWithToggle.java
*            the key to use when persisting the user's preference;
     *            <code>null</code> if you don't want it persisted.
     * @return the dialog, after being closed by the user, which the client can
     *         only call <code>getReturnCode()</code> or
     *         <code>getToggleState()</code>
     */
    public static MessageDialogWithToggle openOkCancelConfirm(Shell parent,
            String title, String message, String toggleMessage,
            boolean toggleState, IPreferenceStore store, String key) {
        MessageDialogWithToggle dialog = new MessageDialogWithToggle(parent,
                title, null, 
                message, QUESTION, new String[] { IDialogConstants.OK_LABEL,
                        IDialogConstants.CANCEL_LABEL }, 0, 
                toggleMessage, toggleState);
        dialog.prefStore = store;
        dialog.prefKey = key;
        dialog.open();
        return dialog;
    }
    /**
     * Convenience method to open a standard warning 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
     * @param toggleMessage
     *            the message for the toggle control, or <code>null</code> for