Make svnrdump suggest --force-interactive when authn fails in
non-interactive mode.

* subversion/svnrdump/svnrdump.c
  (main): Suggest --force-interactive.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1458898 13f79535-47bb-0310-9956-ffa450edef68