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, 0 deletions

diff --git a/diff.h b/diff.h
index 5d50d93a52..7e8000a5d7 100644
--- a/diff.h
+++ b/diff.h
@@ -247,4 +247,6 @@ extern int run_diff_index(struct rev_info *revs, int cached);
 extern int do_diff_cache(const unsigned char *, struct diff_options *);
 extern int diff_flush_patch_id(struct diff_options *, unsigned char *);
 
+extern int diff_result_code(struct diff_options *, int);
+
 #endif /* DIFF_H */