tests/test-diff-newlines

copies: refactor symmetricdifference as _findlimit

We only need to track the lowest revision seen, which makes things simpler.

#!/bin/sh

hg init
python -c 'print "confuse str.splitlines\nembedded\rnewline"' > a
hg ci -Ama -d '1 0'
echo clean diff >> a
hg ci -mb -d '2 0'
hg diff -r0 -r1