was limited by the visible list count, it did not care if the insertion
failed, it didn't maintain the BListItem::fHasSubitems field, neither
fVisible, and it didn't invalidate the latch of the parent, if needed.
* The "add item at end" also did not care if the item should be added to the
visible list, too, it always did.
* AddUnder() would have crashed with a NULL superitem.
* _RemoveItem() now updates the fHasSubitems field as well.
* _SuperitemForIndex() can now return the index of the superitem as well.
* SortItemsUnder() did not check if the "underItem" if the items should be
added to the visible list or not, it also just did.
* SortItemsUnder() now invalidates the part of the visible list that may
have been changed.
* This fixed bug #662, and possibly #663, too (at least I could never
reproduce it).
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@17812 a95241bf-73f2-0310-859d-f6bbb57e9c96
b66c623116