Also hide Cython when hiding setuptools, as setuptools will have imported...

Also hide Cython when hiding setuptools, as setuptools will have imported Cython and Cython references the distutils.Extension. Fixes #488.

CHANGES.txt

@@ -16,6 +16,9 @@ CHANGES
   expose the desired functionality. For example::
 
     $ python -m setuptools.launch setup.py develop
+* Issue #488: Fix dual manifestation of Extension class in
+  extension packages installed as dependencies when Cython
+  is present.
 
 19.5
 ----

setuptools/sandbox.py

@@ -207,8 +207,12 @@ def _needs_hiding(mod_name):
     True
     >>> _needs_hiding('distutils')
     True
+    >>> _needs_hiding('os')
+    False
+    >>> _needs_hiding('Cython')
+    True
     """
-    pattern = re.compile('(setuptools|pkg_resources|distutils)(\.|$)')
+    pattern = re.compile('(setuptools|pkg_resources|distutils|Cython)(\.|$)')
     return bool(pattern.match(mod_name))