Use lib2to3's fix_dict to help with list(dict.items())

Also helps cover dict.viewitems() and friends.

Closes #35
It's in Python 2.7 only and was added primarily for 2to3 so that you could get the view-based results you get in Python 3. I went with the iterator approach as it was the most straight-forward and still gives you the best performance.

I also filed https://bitbucket.org/gutworth/six/issue/92/add-sixviewitems-and-friends to try and get the equivalent functions added to six.