When calling t[1:], for instance, the arguments passed to __getslice__ are
(1, sys.maxsize), which is a pain to deal with, and can even not be an int
(but a long).

If __getslice__ does not exist, __getitem__ is called instead, with argument
slice(1, None, None), which is much more desirable.

__getslice__ is deprecated in python 2.6 anyway.