On the svn-auth-x509 branch, don't fail on certs with v3 extensions.

* subversion/libsvn_subr/x509parse.c
  (x509_skip_ext): New function.
  (svn_x509_parse_cert): Call x509_skip_ext() in the case of v3 certs.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/svn-auth-x509@1605640 13f79535-47bb-0310-9956-ffa450edef68