merge r2995, r2996, r2997, r2998, r3003, r3141, r3210, r3211, r3232:

merge r2995, r2996, r2997, r2998, r3003, r3141, r3210, r3211, r3232:

various SSL fixes and features:

*) $ssl_client_verify
*) "ssl_verify_client ask" was changed to "ssl_verify_client optional"
*) ssl_crl
*) delete OpenSSL pre-0.9.7 compatibility: the sources were not actually
   compatible with OpenSSL 0.9.6 since ssl_session_cache introduction
*) fix memory corruption in $ssl_client_cert
*) issue SNI warning instead of failure: this is too common case
*) use ngx_log_error(), since OpenSSL does not set an error on the failure
*) add SNI support in -V output