* origin/old-proto:
  qa: skip broken ZODB test
  client: fix race with invalidations when starting a new transaction on ZODB 5
  Code clean-up, comment fixes
  master: fix crash in STARTING_BACKUP when connecting to an upstream secondary master
  mysql: workaround for MDEV-20693
  client: inline Application._loadFromCache
  client: replace global load lock by a per-oid one
  client: unindent code
  client: remove load lock in tpc_finish
  qa: check cache in testExternalInvalidation
  qa: comment testExternalInvalidation2