py-future: updated to 0.17.1

What's new in version 0.17.1:
This release address a packaging error because of an erroneous declaration that
any built wheels are universal.

What's new in version 0.17.0:
This is a major bug-fix release, including:
- Fix from collections import ChainMap after install_aliases()
- Fix multiple import from __future__ bug in futurize
- Add support for proper %s formatting of newbytes
- Properly implement iterator protocol for newrange object
- Fix past.translation on read-only file systems
- Fix Tkinter import bug introduced in Python 2.7.4
- Correct TypeError to ValueError in a specific edge case for newrange
- Support inequality tests betwen newstrs and newbytes
- Add type check to __get__ in newsuper
- Fix fix_divsion_safe to support better conversion of complex expressions, and
  skip obvious float division.

As well as a number of corrections to a variety of documentation, and updates to
test infrastructure.

(adam)