Fix restoring expanded URLs

When navigating back or forward in history, DolphinView tells the
KFileItemModel about the expanded URLs which should be restored before
the folder is entered. In this case, the algorithm in the new function
KFileItemModel::setExpanded(const QSet<KUrl>&) does not work. To fix
this, the old function
KFileItemModel::restoreExpandedUrls(const QSet<KUrl>&) is restored.

Unit test included.