* Make SortedStrictSet/SortedStrictMap use a binary search tree (not yet a balanced tree).
* Associate iterators on SortedStrictSet/SortedStrictMap with nodes of the tree.
Invalidate iterators pointing to a node when that node of the set/map is removed.
* Fix sorting order when instantiating StableSortedListSet/SortedStrictSet/SortedStrictMap from unsorted arrays.