Improve mod_ssl's environment variable extraction to correctly handle

Improve mod_ssl's environment variable extraction to correctly handle
DNs with duplicate tags:

* modules/ssl/ssl_engine_vars.c:
  Augment the ssl_var_lookup_ssl_cert_dn_rec table with a flag
  to indicate whether RDNs of the given NID should be extracted
  to the environment.
  (extract_dn, modssl_var_extract_dns): New functions.

* modules/ssl/ssl_private.h (modssl_var_extract_dns): Add prototype.

* modules/ssl/ssl_engine_kernel.c: Remove SSL_*_DN_ from the list
  of variables to insert into the environment.
  (ssl_hook_Fixup): Use modssl_var_extract_dns to insert the
  SSL_*_DN_ variables efficiently and accurately, handling
  certs with duplicate RDN tags correctly.

PR: 45875

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@724717 13f79535-47bb-0310-9956-ffa450edef68