diff: fix "git show -C -C" output when renaming a binary file

diff: fix "git show -C -C" output when renaming a binary file

A bug was introduced in 3e97c7c6af2901cec63bf35fcd43ae3472e24af8
(No diff -b/-w output for all-whitespace changes, Nov 19 2009)
that made the lines:

  diff --git a/bar b/sub/bar
  similarity index 100%
  rename from bar
  rename to sub/bar

disappear from "git show -C -C" output when file bar is a binary
file.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>