Builtin classes list, set, dict reimplemented via B-trees

[Szabolcs Nagy]

IMO sorted dict implementation can be useful, eg. one can get an
interval:
L = D['A' : 'K']

other useful data types:
linkedlist
queue, stack (well deque can do it efficiently in py 2.4)
prioritydict (for graph algorithms)
multimap, multiset (i've never used it but it's in the c++ stl)
mutable string (kind of list/array of chars, but with string functions)

nsz