t4013: add "diff" UI program tests.

Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/t/t4013/diff.diff_-r_--stat_initial..side b/t/t4013/diff.diff_-r_--stat_initial..side
new file mode 100644
index 0000000..245220d
--- /dev/null
+++ b/t/t4013/diff.diff_-r_--stat_initial..side
@@ -0,0 +1,6 @@
+$ git diff -r --stat initial..side
+ dir/sub |    2 ++
+ file0   |    3 +++
+ file3   |    4 ++++
+ 3 files changed, 9 insertions(+), 0 deletions(-)
+$