Merge branch 'jk/diff-honor-wserrhighlight-in-plumbing'

The diff-* plumbing family of subcommands now pay attention to the
diff.wsErrorHighlight configuration, which has been ignored before;
this allows "git add -p" to also show the whitespace problems to
the end user.

* jk/diff-honor-wserrhighlight-in-plumbing:
  diff: move diff.wsErrorHighlight to "basic" config

diff --cc t/t3701-add-interactive.sh
Simple merge