Make svnauth show certificate verification failures in human-readable form.
Make svnauth show certificate verification failures in human-readable form.

Since the certificates are already cached, they've been permanently
accepted. The information displayed shows why the certificate could
not be verified automatically.

* subversion/svnauth/svnauth.c
  (AUTHN_FAILURES_KEY): New macro, copied from ssl_server_trust_providers.c.
  (show_cert_failures): New helper function.
  (list_credentials): Use new helper function to display cert failures.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1501976 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion