Make svn and svnmucc suggest --force-interactive when authn fails in
non-interactive mode.

* subversion/svn/svn.c
  (sub_main): Suggest --force-interactive.

* subversion/svnmucc/svnmucc.c
  (usage): Update help text.
  (main): Suggest --force-interactive.

Suggested by: julianfoad


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1458856 13f79535-47bb-0310-9956-ffa450edef68