This stops difflib from printing many lines which had no change in
them anyway. It also avoids a bug in difflib which fails or hangs
when there are many trailing lines which are all identical.
--HG--
branch : trunk
This currently breaks the test_failuers.py example as that file counts
the number of failures in the demo. But this demo isn't fixed yet so
we'll leave it for now.
--HG--
branch : trunk