This variable contains URL-encoded client SSL certificate.  In contrast
to $ssl_client_cert, it doesn't depend on deprecated header continuation.
The NGX_ESCAPE_URI_COMPONENT variant of encoding is used, so the resulting
variable can be safely used not only in headers, but also as a request
argument.

The $ssl_client_cert variable should be considered deprecated now.
The $ssl_client_raw_cert variable will be eventually renambed back
to $ssl_client_cert.

Pass NGX_FILE_OPEN to ngx_open_file() to fix "The parameter is incorrect"
error on win32 when using the ssl_session_ticket_key directive or loading
a binary geo base.  On UNIX, this change is a no-op.

This, in addition to 1eb753aa8e5e, fixes "upstream zone" on Windows.

The shared objects should generally be allocated from shared memory.
While peers->name and the data it points to allocated from cf->pool
happened to work on UNIX, it broke on Windows.  On UNIX this worked
only because the shared memory zone for upstreams is re-created for
every new configuration.

But on Windows, a worker process does not inherit the address space
of the master process, so the peers->name pointed to data allocated
from cf->pool by the master process, and was invalid.

No functional changes.

In http these checks were changed in a6d6d762c554, though mail module
was missed at that time.  Since then, the stream module was introduced
based on mail, using "== NGX_ERROR" check.

With OpenSSL 1.1.0+, the workaround for handshake buffer size as introduced
in a720f0b0e083 (ticket #413) no longer works, as OpenSSL no longer exposes
handshake buffers, see https://github.com/openssl/openssl/commit/2e7dc7cd688.
Moreover, it is no longer possible to adjust handshake buffers at all now.

To avoid additional RTT if handshake uses more than 4k we now set TCP_NODELAY
on SSL connections before handshake.  While this still results in sub-optimal
network utilization due to incomplete packets being sent, it seems to be
better than nothing.