Log module counterparts are removed as they aren't used often and
there is no need to preserve them for efficiency.

This fixes segfault if stapling was enabled in a server without a certificate
configured (and hence no ssl.ctx).

It was renamed to $body_bytes_sent in nginx 0.3.10 and the old name is
deprecated since then.

This parameter allows to don't require certificate to be signed by
a trusted CA, e.g. if CA certificate isn't known in advance, like in
WebID protocol.

Note that it doesn't add any security unless the certificate is actually
checked to be trusted by some external means (e.g. by a backend).

Patch by Mike Kazantsev, Eric O'Connor.

OCSP response verification is now switched off by default to simplify
configuration, and the ssl_stapling_verify allows to switch it on.

Note that for stapling OCSP response verification isn't something required
as it will be done by a client anyway.  But doing verification on a server
allows to mitigate some attack vectors, most notably stop an attacker from
presenting some specially crafted data to all site clients.

This includes the ssl_stapling_responder directive (defaults to OCSP
responder set in certificate's AIA extension).

OCSP response for a given certificate is requested once we get at least
one connection with certificate_status extension in ClientHello, and
certificate status won't be sent in the connection in question.  This due
to limitations in the OpenSSL API (certificate status callback is blocking).

Note: SSL_CTX_use_certificate_chain_file() was reimplemented as it doesn't
allow to access the certificate loaded via SSL_CTX.

Very basic version without any OCSP responder query code, assuming valid
DER-encoded OCSP response is present in a ssl_stapling_file configured.

Such file might be produced with openssl like this:

openssl ocsp -issuer root.crt -cert domain.crt -respout domain.staple \
             -url http://ocsp.example.com

The directive allows to specify additional trusted Certificate Authority
certificates to be used during certificate verification.  In contrast to
ssl_client_certificate DNs of these cerificates aren't sent to a client
during handshake.

Trusted certificates are loaded regardless of the fact whether client
certificates verification is enabled as the same certificates will be
used for OCSP stapling, during construction of an OCSP request and for
verification of an OCSP response.

The same applies to a CRL (which is now always loaded).