Use svn-diff-args everywhere svn diff is called. This rectifies an
earlier omission.

* contrib/client-side/emacs/dsvn.el
  (svn-call-process): Signature change.
  (svn-log-show-diff): Use svn-diff-args.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1435962 13f79535-47bb-0310-9956-ffa450edef68