TracBrowser: follow-up to [5338], the new expand/collapse, which was a bit buggy (use of toggle show again the content of hidden subfolders, when an ancestor folder is collapsed). This is not a perfect solution, as re-expanding a collapsed folder will show ''all'' the already loaded subtree as expanded. But this is a least a coherent behavior, that one could live with until we implement a solution that will restore the subtree on re-expand in the exact way it was looking before it was collapsed.
