Revamp CRL checking for client and remote servers:

- completely delegate CRL processing to OpenSSL
- introduce a new [Proxy]CARevocationCheck directive
- drop ssl_callback_SSLVerify_CRL from ssl_engine_kernel.c
- remove X509_STORE from modssl_ctx_t
- drop CRL store helper functions from ssl_util_ssl.c
- avoid sending "certificate_expired" SSL alerts to peers
  when the nextUpdate field of a CRL is in the past


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1165056 13f79535-47bb-0310-9956-ffa450edef68