Log Message:
memcached: Update to 1.6.13.

Fixes:
  core: make object cache LIFO
  meta: protocol.txt updates for CAS return
  meta: fix meta delete
  meta: fix CAS ('c') return values
  core: fix use-after-free for text multigets
  Replace OPENSSL_VERSION_NUMBER check with defined(TLS1_3_VERSION) check
    for TLS v1.3 compatibility
  Fix full unit test suite under test_tls
  Track store errors in thread stats
  Fix for failing tests on OS X
  extstore: avoid looping IO queues on submission
  tests: maxconns test when extstore enabled
  core: remove cdefs include from queue.h

New Features:
  The primary feature in development at this time is the proxy. Work can be
  tracked here: https://github.com/memcached/memcached/issues/827 - As this
  stabilizes formal documents will be written. If you're curious about the
  feature please speak up as we are looking for testers and contributors!