LP#1774703 Limit scope of thread locks

LP#1774703 Limit scope of thread locks

Avoid thread contention issues when running this websockets code:

https://github.com/jchampio/apache-websocket

In general, the scope of the thread locking has been dimished, focused
more closely on keeping blocks of reads/writes to the shared recipient
cache running in a single thread at a time.

Thread locks have also been fully removed from the idle timeout thread.
By the time it modifies any shared data, the process is already shutting
down.

Added a few thread safety checks to avoid (the already unlikely and
maybe not even a problem) multiple translator->close() calls just to be
extra safe.

Signed-off-by: Bill Erickson <berickxx@gmail.com>