REL: 1.9.3 release
Merge pull request #6332 from matthew-brett/prepare-1.9.3

MRG: preparations for 1.9.3 release

Backport of 7d6aa8c - gzip fix for Python 3.5
Backport of b08f369 - numpy.distutils patch to help homebrew
Backport of various fixes for Windows builds on modern MSVC.