Provide a new function svn_cert__match_dns_identity() to handling
matching hostnames in X.509 certs as described in RFC 6125.

* subversion/tests/libsvn_subr/dirent_uri-test.c: New tests.

* subversion/include/private/svn_cert.h: New file.

* subversion/libsvn_subr/dirent_uri.c
  (svn_cert__match_dns_identity): New function.

* subversion/libsvn_ra_serf/util.c
  (ssl_server_cert): Use svn_cert__match_dns_identity() instead of
    apr_fnmatch().


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1615211 13f79535-47bb-0310-9956-ffa450edef68