output_difference(): In fancy-diff cases, the way this split expected &

output_difference():  In fancy-diff cases, the way this split expected &
actual output into lines created spurious empty lines at the ends of
each.  Those matched, but the fancy diffs had surprising line counts (1
larger than expected), and tests kept having to slam <BLANKLINE> into the
expected output to account for this.  Using the splitlines() string method
with keepends=True instead accomplishes what was intended directly.