diff: the -w option breaks --exit-code for --raw and other output modes

diff: the -w option breaks --exit-code for --raw and other output modes

The output from "--raw", "--name-status", and "--name-only" modes in
"git diff" does depend on and does not reflect how certain different
contents are considered equal, unlike "--patch" and "--stat" output
modes do, when used with options like "-w" (another way of thinking
about it is that it is not like we recompute the hash of the blob
after removing all whitespaces to show "git diff --raw -w" output).

But the fact that "--raw" and friends ignore "-w" is not a good
excuse for "diff --raw -w --exit-code" to also ignore the request to
report the differences with its exit status.  When run without "-w",
"git diff --exit-code --raw" does report with its exit status the
differences as requested, and we should do the same when run with
"-w", too.

Signed-off-by: Junio C Hamano <gitster@pobox.com>