Fix part of SF bug # 544248 gcc warning in unicodeobject.c

When --enable-unicode=ucs4, need to cast Py_UNICODE to a char

Objects/unicodeobject.c

@@ -6464,7 +6464,7 @@ PyObject *PyUnicode_Format(PyObject *format,
 		PyErr_Format(PyExc_ValueError,
 			     "unsupported format character '%c' (0x%x) "
 			     "at index %i",
-			     (31<=c && c<=126) ? c : '?', 
+			     (31<=c && c<=126) ? (char)c : '?', 
                              c,
 			     (int)(fmt -1 - PyUnicode_AS_UNICODE(uformat)));
 		goto onError;