Merge branch 'master' into t

* master:
  go/*: Cosmetics
  go/xzodb: New package that provides zodb-related utilities shared by drivers  (draft)
  go/zodb/demo: New package that provides base+δ storages overlay
  go/zodb: Provide OpenDriver in addition to Open
  go/zodb/fs1: Report URL with file:// schema included
  go/zodb: Fix Open to detect lack of schema only by ":" instead of by "://"
  go/zodb: Fix IStorage implementation not to deadlock driver if watcher fails
  go/zodb/zeo: Fix it to provide "Close vs watchq" guaranty
  go/zodb/fs1: Fix it to provide "Close vs watchq" guaranty
  go/zodb: Require drivers to close watchq on Close
  go/internal/xtesting: Fix FatalIf to return a helper