memcached: updated to 1.6.20

Memcached 1.6.20

Overview

Lots of fixes and updates for Proxy mode. Optimization for extstore disk flushing to alleviate excess evictions. Changes to meta protocol and smaller fixes.

Fixes

extstore: increase aggressiveness of flush thread
proxy: improve unit test coverage
proxy: random small fixes
proxy: return 'readvalidate' on be read timeout
proxy: don't print null ustats from "stats proxy"
proxy: use connect timeout during retries
proxy: fix flaky test in proxyconfig.t
Add a debian dockerfile, as well as upgrade the autoconf dependency
check for sys/auxv.h
proxy: send CLIENT_ERROR when proper
proxy: print lua error message on reload failure
proxy: rip out io_uring code (to be re-added later)
proxy: overhaul backend error handling: surface error messages to clients
proxy: fix reversal of pipelined backend queries
proxy: add request and buffer memory limits
proxy: restrict functions for lua config vs route
proxy: fix bug ignoring -R setting for proxy reqs
proxy: add conntimeout error

New Features

proxy: add memory accounting tracking

(adam)