Update/fix the build system for Python 3, remove some old/broken/useless code

1) Strongly depend on Cython. Cython.Distutils confirmed present on
win32/linux2 python2.7/python3.3 with cython 0.18.
2) Remove setup3k.py, setup.py is python2/python3 compatible now.
3) Hack around the patch.py step by defining DL_IMPORT at runtime.
TODO: find out when exactly DL_IMPORT was removed and update version
checks accordingly