Changes with nginx 1.7.3 08 Jul 2014
*) Feature: weak entity tags are now preserved on response modifications, and strong ones are changed to weak.
*) Feature: cache revalidation now uses If-None-Match header if possible.
*) Feature: the "ssl_password_file" directive.
*) Bugfix: the If-None-Match request header line was ignored if there was no Last-Modified header in a response returned from cache.
*) Bugfix: "peer closed connection in SSL handshake" messages were logged at "info" level instead of "error" while connecting to backends.
*) Bugfix: in the ngx_http_dav_module module in nginx/Windows.
*) Bugfix: SPDY connections might be closed prematurely if caching was used.