pypy support

PyPy doesn't expose Py_GetArgcArgv. This will detect PyPy and try proc version.

>>>> import setproctitle
Traceback (most recent call last):
  File "<console>", line 1, in <module>
ImportError: unable to load extension module '/devel/pypy-virtualenv/env/site-packages/setproctitle.pypy-20.so': /devel/pypy-virtualenv/env/site-packages/setproctitle.pypy-20.so: undefined symbol: Py_GetArgcArgv
>