Remove compatibility code for collections.defaultdict, in preparation of
dropping support for Python < 2.6.
Remove compatibility code for itertools.permutations, in preparation of
dropping Python2.4 and 2.5 support.
Drop compatibility replacement for unpack_from.
Drop compatibility replacement for 'all'.
Drop compatibility function for namedtuple.
Drop compatibility functions for `hashlib.sha1`.
Drop compatibility wrapper for `parse_qs`.
Drop compatibility wrapper for `SEEK_END` and `SEEK_CUR`.
Update NEWS.