git diff --quiet -w: check and report the status

git diff --quiet -w: check and report the status

The option -w tells the diff machinery to inspect the contents to set the
exit status, instead of checking the blob object level difference alone.
However, --quiet tells the diff machinery not to look at the contents, which
means DIFF_FROM_CONTENTS has no chance to inspect the change.

Work it around by calling diff_flush_patch() with output sent to /dev/null.

Signed-off-by: Larry D'Anna <larry@elder-gods.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>