/**
     * Returns the image descriptor used by the Eclipse Workbench for the given
     * filename. Filename may or may not have path information. e.g. readme.txt and
     * /src/readme.txt are both valid and yield the same result i.e. the image
     * descriptor registered for .txt files.
     * <p>
     * If the argument filename is <code>null</code> then the image descriptor
     * corresponding to a folder is returned. 
     */
    public static ImageDescriptor getFileSystemImageDescriptor(String filename) {
        if (filename == null) {
            return PlatformUI.getWorkbench().getSharedImages().getImageDescriptor(ISharedImages.IMG_OBJ_FOLDER);
        }
        return PlatformUI.getWorkbench().getEditorRegistry().getImageDescriptor(filename);
    }