OpenSSL doesn't check if the negotiated protocol has been announced.
As a result, the client might force using SPDY even if it wasn't
enabled in configuration.

The value of NGX_ERROR, returned from filter handlers, was treated as a generic
upstream error and changed to NGX_HTTP_INTERNAL_SERVER_ERROR before calling
ngx_http_finalize_request().  This resulted in "header already sent" alert
if header was already sent in filter handlers.

The problem appeared in 54e9b83d00f0 (1.7.5).

The following configuration with alias, nested location and try_files
resulted in wrong file being used.  Request "/foo/test.gif" tried to
use "/tmp//foo/test.gif" instead of "/tmp/test.gif":

    location /foo/ {
        alias /tmp/;
        location ~ gif {
            try_files $uri =405;
        }
    }

Additionally, rev. c985d90a8d1f introduced a regression if
the "/tmp//foo/test.gif" file was found (ticket #768).  Resulting URI
was set to "gif?/foo/test.gif", as the code used clcf->name of current
location ("location ~ gif") instead of parent one ("location /foo/").

Fix is to use r->uri instead of clcf->name in all cases in the
ngx_http_core_try_files_phase() function.  It is expected to be
already matched and identical to the clcf->name of the right
location.

If alias was used in a location given by a regular expression,
nginx used to do wrong thing in try_files if a location name (i.e.,
regular expression) was an exact prefix of URI.  The following
configuration triggered a segmentation fault on a request to "/mail":

    location ~ /mail {
        alias /path/to/directory;
        try_files $uri =404;
    }

Reported by Per Hansson.

It's now enough to specify proxy_protocol option in one listen directive to
enable it in all servers listening on the same address/port.  Previously,
the setting from the first directive was always used.

This fixes unbuffered proxying to SSL backends, since it prevents
ngx_ssl_send_chain() from accumulation of request body in the SSL
buffer.

Found by Valgrind.

This helps to avoid suboptimal behavior when a client waits for a control
frame or more data to increase window size, but the frames have been delayed
in the socket buffer.

The delays can be caused by bad interaction between Nagle's algorithm on
nginx side and delayed ACK on the client side or by TCP_CORK/TCP_NOPUSH
if SPDY was working without SSL and sendfile() was used.

The pushing code is now very similar to ngx_http_set_keepalive().