Cache: increased cache header Vary and ETag lengths to 128. This allows to store larger ETag values for proxy_cache_revalidate, including ones generated as SHA256, and cache responses with longer Vary (ticket #826). In particular, this fixes caching of Amazon S3 responses with CORS enabled, which now use "Vary: Origin, Access-Control-Request-Headers, Access-Control-Request-Method". Cache version bumped accordingly.