Merge pull request #1330 from RealRancor/headers_nginx

Add modHeadersAvailable true; to nginx config

admin_manual/installation/nginx_configuration.rst

@@ -94,6 +94,7 @@ Nginx Configuration
      fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
      fastcgi_param PATH_INFO $fastcgi_path_info;
      fastcgi_param HTTPS on;
+     fastcgi_param modHeadersAvailable true; #Avoid sending the security headers twice
      fastcgi_pass php-handler;
      fastcgi_intercept_errors on;
      }