Add ssl_log_xerror() and ssl_log_rxerror(), modeled after ssl_log_cxerror().

Add SSL_X509_NAME_to_string(), which converts an X509 distinguished name
to an RFC 2253 formatted string.
Adapt ssl_log_*error() to make use of SSL_X509_NAME_to_string().


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1172797 13f79535-47bb-0310-9956-ffa450edef68