Incorporate patch review on Flake8Command

* add a note about the setuptools command to README
* don't install the Flake8Command entry point without setuptools
* fix a bug in Flake8Command that might cause double checking
  of files in 'packages'

setup.py

@@ -1,12 +1,14 @@
 import sys
 
 ispy3 = sys.version_info[0] == 3
+issetuptools = False
 
 if ispy3:
     from distutils.core import setup    # NOQA
 else:
     try:
         from setuptools import setup    # NOQA
+        issetuptools = True
     except ImportError:
         from distutils.core import setup   # NOQA
 
@@ -14,6 +16,10 @@ from flake8 import __version__
 
 README = open('README').read()
 
+entry_points = {}
+if issetuptools:
+    entry_points["distutils.commands"] = ["flake8 = flake8.run:Flake8Command"]
+
 setup(
     name="flake8",
     license="MIT",
@@ -24,11 +30,7 @@ setup(
     url="http://bitbucket.org/tarek/flake8",
     packages=["flake8", "flake8.tests"],
     scripts=["flake8/flake8"],
-    entry_points = {
-        "distutils.commands": [
-            "flake8 = flake8.run:Flake8Command",
-        ],
-    },
+    entry_points=entry_points,
     long_description=README,
     classifiers=[
         "Environment :: Console",