Only use setuptools if env set.

setup.py

@@ -10,12 +10,16 @@ from copy import deepcopy
 import os
 from os.path import join, dirname, sep, exists, basename, isdir, abspath
 from os import walk, environ, makedirs, listdir
-from setuptools import setup
 from distutils.extension import Extension
 from distutils.version import LooseVersion
 from collections import OrderedDict
 from time import sleep
 
+if environ.get('KIVY_USE_SETUPTOOLS'):
+    from setuptools import setup
+else:
+    from distutils.core import setup
+
 
 if sys.version > '3':
     PY3 = True