added screed and read_parser streaming testing

Marked as known failing since they currently fail.
Will investigate.

Relevant to #393, #654
What happens if an exception is raised in e.g. io.open? You may need to put everything after thread.start() in a try/finally block, up through the thread.join(). To check this, force an exception (you can just put in 'raise Exception("foo")') after thread.start() and before thread.join() and see what happens when you run the tests.