Add support for OCSP "stapling":

Add support for OCSP "stapling":

* modules/ssl/ssl_util_stapling.c: New file.

* modules/ssl/config.m4, modules/ssl/mod_ssl.dsp: Build it.

* modules/ssl/ssl_toolkit_compat.h: Define HAVE_OCSP_STAPLING if
  OpenSSL is of suitable version (>= 0.9.8g) and capability (TLS
  extension support enabled).

* modules/ssl/mod_ssl.c: Add config directives.

* modules/ssl/ssl_private.h: Add prototypes for new functions.
  (SSLModConfigRec): Add fields for stapling socache instance and
  associated mutex.
  (modssl_ctx_t): Add config fields for stapling.

* modules/ssl/ssl_engine_init.c (ssl_init_Module, ssl_init_Child):
  Call the stapling initialization functions.

* modules/ssl/ssl_engine_config.c: Add config hooks.

* modules/ssl/ssl_scache.c: Create, initialize and destroy the socache
  instance for OCSP responses.

Submitted by: Dr Stephen Henson <shenson oss-institute.org>

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@829619 13f79535-47bb-0310-9956-ffa450edef68