diff --check: minor fixups

There is no reason --exit-code and --check-diff must be mutually
exclusive, so assign different bits to different results and allow them
to be returned from the command.  Introduce diff_result_code() to factor
out the common code to decide final status code based on diffopt
settings and use it everywhere.

Update tests to match the above fix.

Turning pager off when "diff --check" is used is a regression.

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

1 files changed, 2 insertions, 2 deletions

diff --git a/t/t4015-diff-whitespace.sh b/t/t4015-diff-whitespace.sh
index dc538b3e33..757a27abdb 100755
--- a/t/t4015-diff-whitespace.sh
+++ b/t/t4015-diff-whitespace.sh
@@ -148,14 +148,14 @@ test_expect_failure 'check with space before tab in indent' '
 
 '
 
-test_expect_failure '--check and --exit-code are exclusive' '
+test_expect_success '--check and --exit-code are not exclusive' '
 
 	git checkout x &&
 	git diff --check --exit-code
 
 '
 
-test_expect_failure '--check and --quiet are exclusive' '
+test_expect_success '--check and --quiet are not exclusive' '
 
 	git diff --check --quiet