AVL library updated

Hello, I've just updated the AVL library to 2.2: http://homepages.nildram.co.uk/~ahey/HLibs/Data.Tree.AVL/ This version has.. * A few more set manipulation functions. * A kind of cheap but extremely limited zipper which uses node indexing instead of building a path structure on the heap. * Some functions which may end up not modifying a tree (e.g. deletion of non-existing element) now return the original tree (rather than an identical copy with nodes on the search path duplicated). Regards -- Adrian Hey