#18151, part 1: Backport idlelilb portion of Andrew Svetlov's 3.4 patch
changing IOError to OSError (#16715).
#18151 null merge with 3.3.
Issue #15528: Delay importing atexit until weakref.finalize() used.
#17691: test_univnewlines now works with unittest test discovery.  Patch by Zachary Ware.
#17691: merge with 3.3.
#18126: update NumPy links in the documentation.  Patch by Yury V. Zaytsev.
#18126: merge with 3.3.