PyErr_GivenExceptionMatches(): Check for err==NULL and exc==NULL and

return 0 (exceptions don't match).  This means that if an ImportError
is raised because exceptions.py can't be imported, the interpreter
will exit "cleanly" with an error message instead of just core
dumping.

PyErr_SetFromErrnoWithFilename(), PyErr_SetFromWindowsErrWithFilename():
Don't test on Py_UseClassExceptionsFlag.

Python/errors.c

@@ -125,6 +125,10 @@ int
 PyErr_GivenExceptionMatches(err, exc)
      PyObject *err, *exc;
 {
+	if (err == NULL || exc == NULL) {
+		/* maybe caused by "import exceptions" that failed early on */
+		return 0;
+	}
 	if (PyTuple_Check(exc)) {
 		int i, n;
 		n = PyTuple_Size(exc);
@@ -331,7 +335,7 @@ PyErr_SetFromErrnoWithFilename(exc, filename)
 		}
 	}
 #endif
-	if (filename != NULL && Py_UseClassExceptionsFlag)
+	if (filename != NULL)
 		v = Py_BuildValue("(iss)", i, s, filename);
 	else
 		v = Py_BuildValue("(is)", i, s);
@@ -379,7 +383,7 @@ PyObject *PyErr_SetFromWindowsErrWithFilename(
 	/* remove trailing cr/lf and dots */
 	while (len > 0 && (s[len-1] <= ' ' || s[len-1] == '.'))
 		s[--len] = '\0';
-	if (filename != NULL && Py_UseClassExceptionsFlag)
+	if (filename != NULL)
 		v = Py_BuildValue("(iss)", err, s, filename);
 	else
 		v = Py_BuildValue("(is)", err, s);