Changes with nginx 1.7.9 23 Dec 2014

    *) Feature: variables support in the "proxy_cache", "fastcgi_cache",
       "scgi_cache", and "uwsgi_cache" directives.

    *) Feature: variables support in the "expires" directive.

    *) Feature: loading of secret keys from hardware tokens with OpenSSL
       engines.
       Thanks to Dmitrii Pichulin.

    *) Feature: the "autoindex_format" directive.

    *) Bugfix: cache revalidation is now only used for responses with 200
       and 206 status codes.
       Thanks to Piotr Sikora.

    *) Bugfix: the "TE" client request header line was passed to backends
       while proxying.

    *) Bugfix: the "proxy_pass", "fastcgi_pass", "scgi_pass", and
       "uwsgi_pass" directives might not work correctly inside the "if" and
       "limit_except" blocks.

    *) Bugfix: the "proxy_store" directive with the "on" parameter was
       ignored if the "proxy_store" directive with an explicitly specified
       file path was used on a previous level.

    *) Bugfix: nginx could not be built with BoringSSL.
       Thanks to Lukas Tribus.