merge more lines from python3 branch

setup.py

@@ -135,6 +135,9 @@ def __init__(self, *args, **kwargs):
         self.rtool.refactor_dir('docs', write=True) 
         open(checkpoint_fn, 'wta').write('converted')
 
+cmdclass = {}
+if sys.version_info[0] < 3:
+    print(cmdclass)
 def _setup(**kwargs):
 
     # the following hack is taken from scipy's setup.py
@@ -157,7 +160,7 @@ def _setup(**kwargs):
     # numpy sometimes expects this attribute, sometimes not. all seems ok if it's set to none
     if not hasattr(Cython.Distutils.build_ext, 'fcompiler'):
         Cython.Distutils.build_ext.fcompiler = None
-    cmdclass = {'build_ext': Cython.Distutils.build_ext}
+    cmdclass.update({'build_ext': Cython.Distutils.build_ext})
     from numpy import get_include
     include_dirs = [get_include()]
     ext_modules = [Extension("pymor.tools.relations", ["src/pymor/tools/relations.pyx"], include_dirs=include_dirs),
@@ -223,6 +226,7 @@ def setup_package():
                      'Topic :: Scientific/Engineering :: Visualization'],
         license='LICENSE.txt',
         zip_safe=False,
+        cmdclass=cmdclass,
     )
 
     missing = list(_missing(install_suggests.keys()))