changelog: fix the diverted opener to accept more kwargs
The current code prevent the use of `atomictemp` file with the changelog
opener. I do not see a good reason for this limitation.
Differential Revision: https://phab.mercurial-scm.org/D7831
#include <Python.h>
#if PY_MAJOR_VERSION >= 3
#define PYCODETYPE PyObject
#else
#define PYCODETYPE PyCodeObject
#endif
namespace contrib
{
void initpy(const char *cselfpath);
PyObject *pyglobals();
} /* namespace contrib */