mod_ssl: Add SSLClientHelloVars directive which exposes various

mod_ssl: Add SSLClientHelloVars directive which exposes various
ClientHello properties in new SSL_CLIENTHELLO_* variables.

* modules/ssl/ssl_engine_kernel.c (ssl_hook_Fixup_vars): Add
  SSL_CLIENTHELLO_* vars.
  (copy_clienthello_vars): New function.
  (ssl_callback_ClientHello): Call it when needed.

* modules/ssl/ssl_engine_vars.c (ssl_var_lookup_ssl_clienthello): New
  function.
  (ssl_var_lookup_ssl): Call it for SSL_CLIENTHELLO_*.

* modules/ssl/ssl_private.h (modssl_clienthello_vars): Add type.
  (SSLConnRec): Add clienthello_vars pointer.

* modules/ssl/ssl_engine_config.c, modules/ssl/mod_ssl.c: Add handling
  of new SSLClientHelloVars directive.

Submitted by: Charles Smutz <csmutz gmail.com>
Github: closes #483

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1921074 13f79535-47bb-0310-9956-ffa450edef68