osutil.c: Support for py3k added. This patch adds support for py3k in osutil.c. This is accomplished by including a header file responsible for abstracting the API differences between python 2 and python 3. listdir_stat_type is also changed in the following way: A previous call to PyObject_HEAD_INIT is substituted to a call to PyVarObject_HEAD_INIT, which makes the object buildable in both python 2.x and 3.x without weird warnings. After testing on windows, some modifications were also made in the posixfile function, as it calls PyFile_FromFile and PyFile_SetBufSize, which are gone in py3k. In py3k the PyFile_* API is, actually a wrapper over the io module, and code has been adapted accordingly to fit py3k.