Correctly honor exist_ok. Ref #1083.

CHANGES.rst

+v36.1.1
+-------
+
+* #1083: Correct ``py31compat.makedirs`` to correctly honor
+  ``exist_ok`` parameter.
+* #1083: Also use makedirs compatibility throughout setuptools.
+
 v36.1.0
 -------
 

pkg_resources/py31compat.py

@@ -10,7 +10,7 @@ def _makedirs_31(path, exist_ok=False):
     try:
         os.makedirs(path)
     except OSError as exc:
-        if exc.errno != errno.EEXIST:
+        if not exist_ok or exc.errno != errno.EEXIST:
             raise