Fix test-notify for systems without or with a different version of diffstat.
Some diffstat versions say "1 file changed", others "1 files changed".
adding dir/bar
adding foo
dir/bar
foo
adding dir/bar_2
adding foo_2
dir/bar_2
foo_2
adding a
adding c
adding b
adding d
removing a
removing c
recording removal of a as rename to b (100% similar)