Add API to support TLS channel bindings with mod_ssl.

* modules/ssl/mod_ssl.h: Define ssl_get_tls_cb.

* modules/ssl/ssl_engine_vars.c (ssl_get_tls_cb): New function.

Submitted by: Simo Sorce <simo redhat.com>


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1620926 13f79535-47bb-0310-9956-ffa450edef68