exec_file fails completely on Python 3.1 and above

When PY_VERSION_HEX >= 0x03010000, boost::python::exec_file passes an invalid string to Py_RunFile.

The problem is that char* f points to a temporary buffer returned by the UTF conversion routine PyBytes_AsString, but this buffer is deallocated via Py_DECREF before f gets passed to Py_RunFile.

I will create a pull request with a fix shortly.

Locate the boost::python::exec_file implementation and trace the PY_VERSION_HEX >= 0x03010000 path through PyBytes_AsString and Py_RunFile. Confirm the buffer remains valid when Py_RunFile receives it, then exercise exec_file on Python 3.1 or later and verify that the file executes successfully.

Scritto dal modello di indicizzazione a partire dal testo della issue.