Investigate running FFIG from pypy

[jbcoe]

pypy http://pypy.org does not seem to support converting python lists to ctypes.py_objects.

See http://doc.pypy.org/en/latest/discussion/ctypes-implementation.html

This conversion is used by libclang and clang.cindex.py to visit AST nodes.

Investigate this issue, document it and raise a bug which will be closed if/when pypy behaviour changes.