PyErr_SetFromErrnoWithFilename(): New function which supports setting an exception from errno, with a supplied filename (primarily used by IOError and OSError). If class exceptions are used then the exception is instantiated with a 3-tuple: (errno, strerror, filename). For backwards compatibility reasons, if string exceptions are used, filename is ignored. PyErr_SetFromErrno(): Implement in terms of PyErr_SetFromErrnoWithFilename().