Merge branch 'jk/diff-from-contents-fix'

Recently we attempted to improve "git diff -w" and friends to
handle cases where patch output would be suppressed, but it
introduced a bug that emits unnecessary output, which has been
corrected.

* jk/diff-from-contents-fix:
  diff: restore redirection to /dev/null for diff_from_contents

diff --cc diff.c
Simple merge