* <td>
 * URLs that represent servers, shares, or directories require a trailing slash '/'.
 * </td>
 * </tr>
 *
 * </table>
 * 
 * <p>
 * A second constructor argument may be specified to augment the URL
 * for better programmatic control when processing many files under
 * a common base. This is slightly different from the corresponding
 * <code>java.io.File</code> usage; a '/' at the beginning of the second

      collection = ((Multiset<?>) collection).elementSet();
    }
    /*
     * AbstractSet.removeAll(List) has quadratic behavior if the list size
     * is just more than the set's size.  We augment the test by
     * assuming that sets have fast contains() performance, and other
     * collections don't.  See
     * http://code.google.com/p/guava-libraries/issues/detail?id=1013
     */