add simple test for cythonize script

tests/build/cythonize_script.srctree

+'''
+PYTHON ../../../bin/cythonize -i pkg
+PYTHON -c "import pkg.sub.test; assert pkg.sub.test.TEST == 'pkg.sub.test'; assert '.py' not in pkg.sub.test.__file__"
+'''
+
+######## test.py ########
+
+TEST = 'test'
+
+######## pkg/__init__.py ########
+
+######## pkg/test.py ########
+
+TEST = 'pkg.test'
+
+######## pkg/sub/__init__.py ########
+
+######## pkg/sub/test.py ########
+# cython: language_level=3
+
+TEST = 'pkg.sub.test'
+
+ustring = 'abc'
+
+assert isinstance(ustring, unicode)