tests/test-diff-newlines

shrink-revlog: improve performance: use changegroup instead of revisions

Before:
real	0m23.971s

Now:
real	0m4.229s

The only case where the output would be different is if the newer hg was using
a different diff algorithm than used originally.

#!/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