Attempt to solve race-condition which corrupts .pyc files on Windows

This uses of the `atomicwrites` library.

This is very hard to create a reliable test for.

Fix #3008

setup.py

@@ -61,6 +61,7 @@ def main():
         'setuptools',
         'attrs>=17.4.0',
         'more-itertools>=4.0.0',
+        'atomicwrites>=1.0',
     ]
     # if _PYTEST_SETUP_SKIP_PLUGGY_DEP is set, skip installing pluggy;
     # used by tox.ini to test with pluggy master