Previously, when the client address was changed to the one from
the PROXY protocol header, the client port ($remote_port) was
reset to zero.  Now the client port is also changed to the one
from the PROXY protocol header.

It's properly aligned and can hold any supported sockaddr.

OpenSSL 1.0.2+ allows configuring a curve list instead of a single curve
previously supported.  This allows use of different curves depending on
what client supports (as available via the elliptic_curves extension),
and also allows use of different curves in an ECDHE key exchange and
in the ECDSA certificate.

The special value "auto" was introduced (now the default for ssl_ecdh_curve),
which means "use an internal list of curves as available in the OpenSSL
library used".  For versions prior to OpenSSL 1.0.2 it maps to "prime256v1"
as previously used.  The default in 1.0.2b+ prefers prime256v1 as well
(and X25519 in OpenSSL 1.1.0+).

As client vs. server preference of curves is controlled by the
same option as used for ciphers (SSL_OP_CIPHER_SERVER_PREFERENCE),
the ssl_prefer_server_ciphers directive now controls both.

This parameter lets binding the proxy connection to a non-local address.
Upstream will see the connection as coming from that address.
When used with $remote_addr, upstream will accept the connection from real
client address.

Example:

    proxy_bind $remote_addr transparent;

This prevents forming empty records out of such buffers.  Particularly it fixes
double end-of-stream records with chunked transfer encoding, or when HTTP/2 is
used and the END_STREAM flag has been sent without data.  In both cases there
is an empty buffer at the end of the request body chain with the "last_buf"
flag set.

The canonical libfcgi, as well as php implementation, tolerates such records,
while the HHVM parser is more strict and drops the connection (ticket #950).