[test] Add a trivial test for "wdoc" view We just make sure it gets rendered without errors (which wasn't the case before the previous patch). It does not work on Python 3; this will be fixed in next changeset.

[py3] Open rst file in text mode in wdoc view Otherwise, UStringIO complains that it receives bytes.

[ext/rest] Drop "handle_io_errors" argument to docutils' FileInput This argument is deprecated and ignore in docutils since version 0.10. Besides, its default value is None which is the same as we passed.