Pure Python version of collections.deque()

[Raymond Hettinger]

FWIW, I've posted a recipe for a pure python version of Py2.4's
collections.deque().  It is a drop-in replacement and should work with
Py2.0 and later:

   http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/259179


Raymond Hettinger