Changes with nginx 1.11.10 14 Feb 2017
*) Change: cache header format has been changed, previously cached responses will be invalidated.
*) Feature: support of "stale-while-revalidate" and "stale-if-error" extensions in the "Cache-Control" backend response header line.
*) Feature: the "proxy_cache_background_update", "fastcgi_cache_background_update", "scgi_cache_background_update", and "uwsgi_cache_background_update" directives.
*) Feature: nginx is now able to cache responses with the "Vary" header line up to 128 characters long (instead of 42 characters in previous versions).
*) Feature: the "build" parameter of the "server_tokens" directive. Thanks to Tom Thorogood.
*) Bugfix: "[crit] SSL_write() failed" messages might appear in logs when handling requests with the "Expect: 100-continue" request header line.
*) Bugfix: the ngx_http_slice_module did not work in named locations.
*) Bugfix: a segmentation fault might occur in a worker process when using AIO after an "X-Accel-Redirect" redirection.
*) Bugfix: reduced memory consumption for long-lived requests using gzipping.