misc bug fixes

- Remove spammy warning message from event streamer.
- Fix panic on double-close of memcache connection.
- Disallow non-identifier table names even if it's back-quoted.
query service: load schema safety

Add some safety around how we load schema by back-quoting table
names. This will prevent unexpected crashes if a badly-named
table makes it through.
Merge branch 'suguwork'