update setup.py script to use cythonize()

--HG--
extra : rebase_source : 6494c60e7f79a9cc85fe72a7adf325557f6de2be

Demos/callback/Setup.py

 from distutils.core import setup
 from distutils.extension import Extension
-from Cython.Distutils import build_ext
+from Cython.Build import cythonize
 
 setup(
   name = 'callback',
-  ext_modules=[ 
+  ext_modules=cythonize([
     Extension("cheese", ["cheese.pyx", "cheesefinder.c"]),
-    ],
-  cmdclass = {'build_ext': build_ext}
+    ]),
 )